Who saved that file?

I need to find out who saved a file on our server. Is this possible? In other words, there are some files that shouldn’t be there, and I need to know who put them there. Or which computer they used to save them would be fine, too. We have a Win2k server, clients are Win98 and XP. I’m sure the server ‘knows’ where the file came from, I just can’t figure out how to get it to tell me! Thanks.