Data Loss - Things suddenly disappeared!

Hi, for some bizarre reason a LOT of data on my iMac seems to have vanished. I have no idea why, my hard drive has the same amount of free space as it used to so this tells me it must be there somewhere. My Music/Video library has gone along with general setting e.g mouse/dock preferences were reset to default and all my Firefox bookmarks have gone too. Not so good Upon going into my music folder instead of finding all the albums in iTunes music there is nothing, same with Videos. The folders that were on my desktop had disappeared too, but I searched for them in the HDD and found them.

Basically everything has gone and I don't know where it is, however I think it is still there due to my HDD space remaining the same.
I was installing a game on WinXP through Parallels 4.0 when things starting acting slightly strange for example downloads from Firefox would not show on the Desktop where I saved them, but I could search for them and find them and it would show them as being on the desktop, just not visible for some reason.
I'm about to try a data recovery tool. Any suggestions on a good free one?
Any info/advice is much appreciated - I'm sure I'm not the only one who has suffered from this sort of thing!
I hope all that made sense. Thank you for your help and time (and for reading through this massive post)

Cheers

Did you by any chance change your short name or the name of your user folder?
Look in /Users, how many folders are there?

I think that's it!
It's always the simple thing.... I think I changed the name of my home folder.
I've changed it back now. Shall reboot and see if my iTunes etc. are back to normal.
Thanks!

Yeah that worked - Cheers!!!!

The bill is in the mail