Deleting the event log on server2003

I have been told by auditors to keep backups of event logs. So what I thought I would do is periodically go into the C:windows\system32\config and copy the log file then delete it so the size wouldnt get to big (I have limited HD space on C:). But when I try to delete the log file it says I cant because its currently in use. I assume its just a process I need to turn off but I did a search on google and didnt turn up anything. If anyone knows how to delete the file or has a better way to achomplish the same thing I would appreciate it. Im running Server 2003 SP1.

Thanks