Go read Digital Foundry if you want really deep hardware annalysis (Link [http://www.eurogamer.net/digitalfoundry]).
From what I understand, the 360 Whatever-the-hell-it's-called graphics card is better than the PS3's RSX and has more... I forgot the word, but it can send more information faster. Also the MS design tools are able to.. Wow, I'm not remembering any big words right now, well, they make it easier for the system to produce results. The PS3 could have better graphics, but developers normally don't use the cell as much as exclusive PS3 developers do (See Uncharted 2), which has tons of power but is almost never really used in most cross-platform games, cause that would require more work. And I'm forgetting something, but oh well.