Ritchey compacts will work with your existing bottom bracket, other models would generally require replacing the bottom bracket.

However, you might want to consider just going for a wider range cassette, such as my Century Special 13-30 or one of the Cyclotouriste 13-34s. (Your present rear derailer should work fine with the 30, but you would need a new rear derailer to go bigger. However, suitable derailers are dirt cheap, as little as $20.)

Sheldon "http://harriscyclery.com/9" Brown