Cool. Not too many things will let you convert AIFF or CDDA data directly to MP3 anyway, so you did the right thing by getting it to hard drive first. Also, by having it stored there, if something happens in the conversion, you can always just do another conversion without having to run the tape.
Anyway, the Blade Encoder and Blade Helper work very well. They are free! And free is a very good price. Not many bells and whistles with these two programs, just good, solid mp3 conversions.
Download and install the Encoder first. Then install Helper. Use Helper to select the .wav files you want to convert. It will let you select multiple files at once, and will let you set things like kbs, system priorities, where to save the new file, etc...128kbs is the standard conversion that is done, but for much better fidelity, without jacking the file size too large, try 192kbs. After 192, you really don't get much improved quality that you are gonna notice except through really good monitors. If you are going to post this stuff on a mp3 download site, they usually want it at 128kbs though.
Anyway, once everything is installed, just select the files you want to convert, and hit start, and away it goes! Very simple. Also be sure to download a Ripper program. This will allow you to digitally transfer anything from a audio CD to your hard drive via the CD Rom drive. Very cool program. But if you already got a SCSI CD Rom drive, you won't need it as it will already retreive data from the CD Rom drive via the ribbon strip (which only takes digital data) and route it to wherever. Anyway, have fun!
Ed