if you can't design on your own, use ready-mades! Use KEYNOTE:

but WAIT! We want to make a VIDEO-Cast, no Slideshow?!

This is correct - but you can use KEYNOTE for 'designing' charts, or complete videos. Here's how:

Choose a template you like (btw: there're tons of free or commercial additional templates!), and choose as size 960x540 (as you probably know, iM09 down-scales 'fullHD' anyhow), or, if you're using 720p material as me, 1280x720.

Create your charts - keep in mind: in iMovie09 you'll probably add a 'narration'! Keep in mind: don't irritate you audience with too complex video, when audio is important!

Spend some time reading & watching this wonderful website PRESENTATION-ZEN.

KEYNOTE offers some effects, iMovie doesn't - but don't do too much eye-candy! For me, an effect is an emphasis - it focusses a point, stresses some topic. use it wisely.

KEYNOTE allows to 'build' a chart - same trick, we use with stills ... /link/

After the presentation is done, all effects added, timing is ok, we export:

File/Export/QT/CUSTOM .. (and FIXED TIMING) ... 

Finally, the right codec .. 

and, NO, HDV ≠ HDef .. HDV is a special Codec with some special setting.. click OTHER .. 

The framerate depends on your settings of your iM-Project, rule of thumb: US=30, World=25.

When done, you get a very large .mov you can 'Import Movie' into iMovie09 and instantly use with superb quality. 

And KEYNOTE can do even more: 

It allows to export single charts as jpg, we can use as inserts, pic-in-pic or as background for some green-screen recording: 

KEYNOTE jpg plus PIP 

KEYNOTE Template as Green-Screen Backdrop

KEYNOTE Effect in a VidCast done with iMovie09