You can do a side-by-side comparison of camera specs at
http://www.dpreview.com/reviews/sidebyside.asp ... like this:
http://www.dpreview.com/reviews/comp...n_d60&show=all
But specs will only tell you so much... on paper they're pretty similar: XSi is 12MP, D60 is 10MP; XSi has a slightly larger viewscreen (3.0" vs. 2.5" on the D60); both do ISO 100 to 1600, both have 1/4000s max shutter speed, both use SD/SDHC memory, etc. etc. etc.
You'll get some guys who will argue the differences between CMOS and CCD sensors, the benefits of Canon vs. Nikon lens systems, and other such inanities til they're blue in the face, but at the end of the day, to 99% of the users out there, there's really no appreciable difference in the final product.
What DOES differ from a user's perspective, is ergonomics. The feel of the camera, the way you hold it, how easy it is for you to operate. If a camera is uncomfortable for you to hold, or if the controls are in weird places for you, or the menus are a pain to navigate, then you're less likely to ENJOY using it, and it's more likely to just sit on a shelf rather than getting used... and if that happens, the minute, arguable differences in the specs become completely meaningless.
A good example was the Rebel XT (aka 350D), which a lot of people with bigger hands found too small to hold and operate comfortably. For people with smaller hands though, it was great.
The secret, once you've narrowed it down to two or three different choices, is to go to the store and actually handle the cameras. Play with them, operate them, see how they feel to you, see how comfortable you are navigating them. Make sure you'll actually enjoy USING the camera, rather than getting uptight about the minor differences in numbers.
Note: the one major technology difference between the XSi and the D60 is that the XSi has the LiveView function, which is something not a lot of DSLRs have yet. For some people, that's the deal-maker... for others, it's not so important. Only your own needs will determine whether it is for you.