Hopefully it wasn't your primary hard drive. Every time you download a file, install a program, load/refresh a webpage, or do anything that involves CPU/mem usage, it decreases the chances of recovering the full file. When something gets deleted, the data stays there but now those physical portions are flagged to be overwritten onto, just like the rest of the free space on your drive.
If it's a secondary or slave drive then you should be okay as long as you don't use it, but if it's not then your best bet would be to remove the hard drive and hook it up as a slave drive to another PC, which is the best way to use those recovery programs. If not then make sure you try the recovery process as soon as absolutely possible and try not to restart the PC much or have any unnecessary activity, and your chances should be pretty good.