So did you lose the files from your hard drive or from your memory card of the camera? If you lost them from your hard drive on your computer, they may be gone, but not forgotten. Try a free download called, PC inspector File Recovery. You'll have to Google it, or you may find it on download.net. But as Jcharcalla said, in Windows, if you delete a file from your pc, windows, basically says to itself, "I can use these sectors for whatever I need". Once deleted, windows can then save anything to any space not already allocated for another program. Therefore, you could technically delete something then recover it years later, provided windows didn't happen to choose that space to save a lot of other information in the mean time. The hard drive just searches for free, unallocated space when saving something new, and doesn't necessarily spin the hard drive to find the space. It's possible that your files haven't been overwritten yet. I'm not sure how a memory card goes about this process though.
In the future (hindsight 20/20) you will want to back up photos like anything else you find important to at least a couple of different places. I have mine on one hard drive, then again on an external hard drive, then again on DVD. Hard drives are inexpensive now, and you can expect to spend a dollar/gig of space roughly. That is, 100gb HD can cost about $100 (for external...even cheaper for internal). I wouldn't waste money on a "pen-drive" or thumb-drive (those little usb drives you can carry in your pocket) when a good HD is so cheap provided you don't need that type of portability. You can also get a decent dvd burner for about $60 now to back files up to that if you wish. Ideally, if it is "really" important stuff to back up, you want them off-site incase of fire, theft, natural disaster like an online site, or backup your stuff periodically to an external drive and leave it at a friends house.
just my .02