Using Ram pulled from new iMac in an old iMac? My parents have an iMac circa 2007. Documentation says that this model should use this type of RAM:

Memory: DDR2 PC2-5300
Memory Type: DDR2 PC2-5300, DDR2 (non-ECC)
Maximum Memory: 4GB 

I've got a couple of 2GB RAM chips lying around that I just pulled from my "new" iMac. The info on the chips reads:

2GB 1Rx8 PC3

Will these work in my parent's iMac, or am I just asking for trouble?

Thanks!
No.

Those new iMacs are using DDR3, and it won't even fit.

DDR2 are pretty cheap right now, you can get some off the Internet.