Bicycle Mechanics - Replacing old Shimano RX100 cassette?

I have an old Cannondale R400 w/ RX100 crankset and cassette. As the cassette is 12-23, I'd like to replace it w/ at least 12-27, or even 12-30 (hills!). I'm happy to stay w/ 7 sprockets.

Is this even possible? I have read that most shimano cassettes are interchangable. In particular, nashbar has a Shimano IG60 7sp 11x30 casette:
http://www.nashbar.com/profile.cfm?category=87&subcategory=1109&brand=&sku=2940&storetype=&estoreid=&pagename=

Could I put this on?

I have an old Cannondale R400 w/ RX100 crankset and cassette. As the cassette is 12-23, I'd like to replace it w/ at least 12-27, or even 12-30 (hills!). I'm happy to stay w/ 7 sprockets.

Is this even possible? I have read that most shimano cassettes are interchangable. In particular, nashbar has a Shimano IG60 7sp 11x30 casette:
http://www.nashbar.com/profile.cfm?category=87&subcategory=1109&brand=&sku=2940&storetype=&estoreid=&pagename=

Could I put this on? Depends. If your casette is uniglide with a screw on first cog,no. If your casette is A hyperglide, yes,but you would be better off looking for a HG casette,as the IG was designed with a ramping system to assist shifting in both diredctions,and used an IG chain. Your rear derailer may also be beyond it's speced capacity with a 30 cog,but will probably still work by tweaking the B tension screw. You might need a longer chain too. Another point is that if you need a 30 you probably don't need an 11.The ratio jumps stink. There are HG 12x28 and 13x30 7 speeds available available.

My guess is that your low gear limit on an RX100 is going to be a 26 or 27. You should replace the chain when you put a new cassette on. If you don't have the tools, don't get the parts from Nashbar, just go to your LBS and have them do it. That way they get to make sure that the new chain is the right length and that the cassette and chain match each other.

My guess is that your low gear limit on an RX100 is going to be a 26 or 27.
Bad guess.

Flipping through last years QBP I find only a 13-26 7s cassette that would work on your bike(Without changing any thing else) If you want to change your rear der. as well, to an MTB type you can go as wide as an 11-34(Made by sunrace) or 13-34(Shimano)

Flipping through last years QBP I find only a 13-26 7s cassette that would work on your bike(Without changing any thing else) If you want to change your rear der. as well, to an MTB type you can go as wide as an 11-34(Made by sunrace) or 13-34(Shimano) His RD was speced for a 28 large cog and will handle a 30. 7 speed road casettes went to a 28 cog. I've got a 7 speed DA RD that was only speced for a 26 and it handles a 28 easily.Harris cyclery has the 7 speed casettes I mentioned.

Ah, well, you win the prize then. :)