Assuming you ripped them from CD to start with then don't convert them, rip them again from the CD using windows media player, make sure you have media player set to rib to 128kbs MP3 (or CD quality) and also make sure you have a internet connection when you rip them.
If you rip them again then the tags embedded in the files that contain information about the track will all be correct. Trust me, once you start using MP3's properly you soon realise that getting the tagging correct is very important (unless you want a MP3 player full of tracks that just say "unknown artist"