Picasa doesn't use the printer defaults from Windows - you must set up all your printing options up in the print dialog.
If you are having printing problems, the first thing to check is that you have the right printer selected and set up in the Picasa Printer screen.
If a digital photo is going to exactly fit the paper it is to be printed on, it must have the proper "aspect ratio." This means the length to width ratio of the photo must be exactly the same as the length to width ratio of the final photo. If it does not have the proper aspect ratio, either the edges will be cut off or there will be white space in one direction.
Example: 4x6 photo paper has a .667 aspect ratio. If the digital photo has an aspect ratio of .667 also, when the digital photo is expanded or contracted until it's long dimension exactly fills the 6 inch dimension, it's width dimension will exactly fill the 4 inch dimension of the paper. If the digital photo had an aspect ratio of .5, when the length was adjusted to fill the 6 inch height of the paper, the width would only be 3 inches, leaving a .5 inch white space on each side, or if the width was adjusted to fill the 4 inch width of the paper, the height would be 8 inches and 1 inch would have to be cut off the top and bottom of the photo to fit the 6 inch height.
The first thing to do is to decide if you want to Crop the photo so it will have the right length to width ratio for your printed photo, or if you want Picasa to guess at how to crop it during printing.
If you want to control the cropping, do this:
In the Thumbnail view double-click on the photo thumbnail to bring it up in the editor.
The edit controls should be visible to the left of the photo to be edited, if not, go to the View menu and select Show Edit Controls.
Click on the "Crop" button, then select 4X6 or whatever size you want to print from the crop size pull-down menu.
Draw a box around the area of the photo you want to show by holding down the left mouse button and drawing a box. You can pull the sides of the box to get it to the right size.
Click the Apply button when the photo is right and see the result. Uncrop or ReCrop to try again until you are happy with what is cut off.
Note: If you don't want to have your Original photo cropped but want to keep a copy of the cropped version, do the following:
Once the photo is cropped the way you want it, go to the File menu and select "Save a Copy". This will save a copy of the cropped photo in the same folder as the original photo. The cropped version will be at the end of the folder and will have the same name as the original with "-001" appended to the name.
After you have saved the copy, edit the original again and Undo the crop by clicking the "Undo Crop" button in the edit tools panel.
Back in Library View, hit the End key to go to the end of the folder and find the cropped copies.
Select Photos and Start Printer Dialog:
To select photos to print use any of the standard Picasa methods:
Hold down the Ctrl key and click on each photo in the folder to select them.
Or draw a box around the photos to select them.
Or click the first photo of a set, hold down the Shift key and click the last Photo of the set.
Or to select all in a folder, click in the folder then type Ctrl+A (select all).
If you want to select photos from multiple folders, select the photos you want in the first folder, then click the little green push pin icon in the lower left corner of the Picasa screen to hold them in the tray. Next select more and repeat until all you want are selected.
After selecting them, the Photo(s) to be Printed will be in the tray at the bottom left.
Click on the Print button near the bottom center of the Picasa screen.
In the Print dialog box at the top, Click on the 4x6 button (or whatever size you are printing).
There is also a "Full Size" button which should print out to whatever paper size you select.
The above selects the size of the photo, not the paper size.
Note: If the size Photo you want to print is not one of the selections among the 6 at the top of the print screen, Go to the Tools menu -> Options -> Printing tab. At the top of the Printing options select one of the buttons you don't use much and in the pull-down list, select the print size you want for that button. The button will be redefined in the Print dialog.
Click the Printer Button on the Left side of the Print dialog box.
Select your Printer if it is not already selected.
Note: in some instances a printer will appear more than once in printer selections.
If one of the selections fails to print or prints incorrectly, try selecting the other instance.
Click on the Printer Setup button on the left side of the Printer dialog box just below the Printer button.
Set up your Printer Paper size, Paper type, Quality, and everything else about your printer.
Make sure the Printer paper orientation is set for the paper not the photo. Picasa automatically rotates the photo as necessary
Orientation should almost always be Portrait because that is the way the paper is loaded in most printers.
You may have to go into Advanced setup mode to get everything set right
Make sure the printer is set to border-less printing if you don't want borders.
Make sure the printer is set to Color printing and not grey scale.
Click Ok or Apply or however you accept the settings
Note: The Printer Setup steps are Critical! because Picasa uses this printer setup, not whatever the printer is set to by default in Windows.... You may have to go into advanced setup. The above steps select the size of the Paper, not the Photo size.
The Preview screen (center) should now show your photo on your paper selection. If it isn't the way you like it, go back to printer setup and get the printer set to the right size paper and border etc.
If you didn't crop the photo to the right ratio before printing, try the "Shrink to fit" and "Crop to Fit" buttons to see Picasa's ideas on how to make the photo fit on the page.
Look at the border and text options to make sure they are set to none, unless you want borders or text.
Select the number of copies you want of each photo using the -/+ Copies buttons.
Note: If you select a paper size that will allow more than one photo per page, (with a small margin between each photo), Picasa will print multiple photos per page.
Example: 2 4x6 photos will print on a sheet of 8.5x11 paper. ( 2 5x7 photos will not fit on 8x10 paper because there is no space between the 5 inch wide photos on 10" wide paper, but they will both fit on 8.5x11 paper)
When the preview looks right, hit Print.