erm, there's a couple of ways you can do this.... but the success rate is pretty low for both.
You can try the Repair Archive feature within WinRAR, or if it's a large archive and the person who archived it also made some PAR files, you can use another app along with the relevant PAR file to repair your borked RAR file. Can't remember the name off the top of my head but will find it if necessary.
Does that make sense..? Too many rhyming words for me. Rar, Par, Schmarr
