You should probably put more detailed info up before this forum can reply properly. What type of computer do you have (Platform, OS release, CPU, RAM, Graphics card--that sort of stuff would help if you know it)? Also, do you plan on scanning hand drawn sketches, or are have they been created using a basic drawing program? Do you have a pen and tablet, or are you going to use a mouse? How serious are you about detailing your sketches?
Adobe Illustrator seems to be the best program for your task, but it can only be useful if your computer can handle it, and is better (but not limited) suited for pen and tablet work. The "catch" is its price tag and steep learning curve to those who are unfamiliar to digital art programs.
Photoshop 7 and CS can do some of the things that Illustrator does, but are better suited for raster graphic manipulation. Also, for the price, photoshop 7 is a much better deal than CS. Most of the differences between the two releases are not very important for non-commercial work. You can easily get by without them.