so i wanted to post this up as it has to do with my last two topics about chains and cassettes. the space between the rear dropouts and how many gears your bike has are very much related, especially when converting a bike to new gearing. It is important to know your target spacing and how to work with what you're dealt.
i'm posting this article up also from sheldon's site on cold-setting your frame to help add more references in this section of the forum. this info should come in handy while wrenching at the shop.
http://sheldonbrown.com/frame-spacing.htmltis the season to get on your crotch
- tomb