A pity, you discovered some more problems.
233MHz Rev.A.
You can update rev. A to B, by installing additional VRAM (SG-RAM). They look like Laptop-SDRAM (SO-Dimms), but have the cut in another position (ok, this description is misleading, one could mix them up with DDR-SO-Dimms..., wel I guess you will find them on Ebay).
Cheapest wway to get them is searching for "kg RAM" or "ounces RAM" or "kg memory" or "RAM recycling". You can buy a for example 5kg RAM, which is declared as faulty/untested. Of course you would have to test them...
You can put them aside, and everytime you need RAM you test one. Keep those that are defective and sell them again on Ebay or bring them to a local recycler (in Germany the price for 1kg RAM is 22,50EUR, at the time. I do not know, if you have an option where you live).
You can test the RAM with this
http://www.command-tab.com/2008/01/11/how-to-test-ram-under-mac-os-x/
(this is very time consuming, so if you want to be honest to the buyers, you could also just drop them in and test, if the iMac powers up and recognizes the RAM. Then you would have to tell the buyer, that you did not test the added RAM further, but booting up etc.)
Maybe you find two 512MB Sticks for your main machine as well.