Everyone's done it, accidentally recorded over something with their video camera. Or even if it wasn't accidental, don't you just sometimes with you could have some of those outtakes back to watch and laugh at. Well, before the digital age--if you can remember that far back--people recorded on VHS tapes. Besides being bulky and temperamental, VHS tapes also don't store data once its recorded over, and therefore it can't be recovered.
Video recovery of a recorded-over VHS tape is not feasible, so don't get too fixated on recovering that old footage. For a variety of technical reasons, VHS tapes aren't able to store video data once its been recorded over, in fact when a VHS tape records over something it erases the footage that previously occupied the tape.
If something was recorded over on a tape that you really think you can't live without you can try consulting a professional service that specialises in videotape repair, recovery and restoration, however the chances that much of the recorded over material can be salvaged is very slim and the process is usually rather pricey, so be prepared to pony up some serious cash.
Transfer all your VHS recordings to backup tapes, or better yet transfer them to a digital format. By doing this you will not only avoid the embarrassing and painful possibility of recording over them, but you will preserve the video at its current quality. Anyone who has watched an old VHS knows that over time VHS recordings lose their quality. Although transferring video from VHS can be a time consuming process, if you care about the content of the video it's also a worthwhile one.
Tapes that are old, damaged or not working for some other reason such as the presence of mould or dust can often be salvaged. Whatever you do, don't try to play a VHS that is not in good condition, as this could worsen the situation. The best thing to do is contact your local video repair service and have them look at the tapes. Since damaged and dated VHS tapes are common these days the procedure is relatively common and shouldn't put you out too much.
Take advantage of modern technology and buy a digital or miniDV camcorder, which can easily be transferred to digital format. By doing this you don't have to worry about recording over valuable footage, or about the gradual loss of quality that VHS tapes experience.