I made a similar change to the cassette for my road bike last year:

http://forums.teamestrogen.com/showthread.php?t=55780

The short version is: I went from 11/26 to 11/32. I did have to change the derailleur, from short cage to mid-cage so you might be okay with the one you currently have.

At the time one of my friends encouraged me to get cassette with a 36 cog. I think that would have necessitated a long-cage derailleur but am not sure.

My components are all SRAM, and IIRC I was able to find good information about compatibility with cassettes and derailleurs on their website.

p.s. I am SO happy that I made these changes. Totally worth it.