That's for the G5 iMac, no?
The Newer ones are Intel Core 2 Duo and the RAM they use are 667MHz SODIMM, not a PC4200 like what's describe.
However, I can't seem to find any article on Apple with regards to upgrading them C2D ones. I'm pretty sure you can up BOTH memory stick i.e. 1GB RAM x 2 = 2GB instead on just able to upgrading 1 stick with the other 512MB built into the logic board (which is a complete hassle to upgrade youself)
Edit:
There - that's for the late 2006 models (since the 24inch basically)
http://docs.info.apple.com/article.html?artnum=303084