How to recover files after installing Windows 7?

I installed windows 7 on my computer and all of my files are gone. I have been reading online that you can install an undelete program, but I'm still not sure, the other option was to take the hard drive out and connect it as a slave drive to another computer and use a undelete program on the computer. Please help me, I dont want to mess this up anymore that it is. What should I do, and can I recover the files? I dont know if the hard drive was formatted during installation. I dont think it was. Please help...

 

If you did an upgrade from Vista, you should still have your files. If you did a custom install which is required if moving from XP, your files are gone because Windows 7 formatted the drive.