Can any body tells me where I can find the free full version of Mp3 to wav and wav to mp3 converter. Thanks..

This one seems pretty good:
River Past Wave@MP3 - Overview

Just click download on the left and give it a go.
I would recommend giving it a scan with whatever virus tools you have before you run it, though.

I have used BonkEnc for a good long while now:

SourceForge.net: Files

You'll want the BonkEnc-1.0.3.exe link a little ways down the page, assuming you're on Windows.

100% free software (both free as in speech and free as in beer)