Currently one goes to the purchasing office in 54 Mulford (enter from the back of the building, the inside of the C shape) to get either check reimbursements or travel reimbursements.  You see different people for the two things, and there are different forms for the two types of reimbursements.  Check reimbursements can take a very long time to go through the entire bureaucracy, so make sure you can afford to wait to be reimbursed for something before you buy it.  This is another area that may change drastically in January 2010 when the department is 'centralized.'