Depending on what you use to rip, you will probably need LAME. Go here and get a LAME bundle. Extract and put the folder in Program Files.
EAC is a good ripping choice but not as easy as some others. Go here and get it.
Setting up EAC needs a few extra settings than the "one click" programs. Here are some instructions.
Use EAC if you are anal about your MP3's or are having trouble getting good rips.