Are there any decent free converters that can change CDA to MP3??

I just started using FreeRip.
http://www.freerip.com/

i reckon dbpoweramp.com will work, you might have to d/l a plug in... but i'm pretty sure it'll do the trick.

Why not use WMP 10 or 11? Both of them have MP3 encoding.

The file is on my HardDisk, its not on CD.. Will those still be useful?

Nope, and normally CDA files can't be stored on a hard drive, are you sure they're valid files? What's the file size(s)?

I've found something that claims to be just what you wanted though.
http://www.nesoft.org/alt-cda-mp3-converter.shtml#download
There's a 15 day trial, and I have no idea how good it is at encoding.