Yeah, I had that problem. Turns out Wave Editor is just a Trial of some kind and doesn't let you carry on using it after a certain period.
As for a new wave editor which I use and can't congratulate the freeware open source program enough:
Its great for splitting tracks, but if you look in the webpage you will find if you haven't got the lame_enc.dll file, you will have to download it from here:
This allows you to export in MP3's if you haven't got something like Winamp that has it within the program. Just do a search in Windows if your not sure.
You'll find the option to browse for the lame_enc.dll file within Options after selecting MP3 as a export option
EDIT: It also allows you to record, add sound effects (echo, flanger etc), etc.
Hope this helps