Hey guys! I really could do with some help. I have a 4GB zip file which will not open or extract at all. In 7zip winzip or winrar. I get the following message:

"unexpected end of archive"

What on earth can be done to save my rare data? I didn't download it, it was compiled on my old computer many moons ago.

If anyone can help get my things back I will reward them by closing my eyes and attempting to draw on paint anything you desire! :P

It would appear the archive has been damaged, either aggressively compressed and the current tools can't read it, or faulty storage medium, you can try again and again, try with either older versions (although new ones should support legacy), latest versions or concede to the fact that your data is lost.

Yes, it sounds as though the archive has been corrupted (is it on a DVD?).
Sadly there's nothing you can do now to restore it back to a working archive. The best you could do is to partially extract it and see what you get. If it's a collection of a number of files you should be able to use all of them except the one(s) that is/are corrupted. If it's one large file then you'll have trouble using it. Let us know more details because they may change how to recover the data.

Where is the archive (DVD or hard drive)?
What is in the archive (i.e. a collection of files or one file? What filetype(s)?)?

Something which could come in handy (for the future) is creating a parity recovery set for your backups (using a program such as QuickPar). By creating recovery volumes you will be able to fix an amount of damage done to the original file (in the transit or storage). Sadly this cannot be applied retrospectively, you would need to have the original archive to create recovery.

You can try to use the Tools -> Repair archive function in WinRAR, and see if it's able to fix part of your zip file.

Or try this program: http://www.diskinternals.com/zip-repair/

It will all depend on how and what with, the original archive was compressed with, although, I wouldn't hold out too much hope, damaged archives are difficult to fix.