dmorr,
When this starts happening, it's usually time to "clean-up" your hard-drive. First thing to check is available hard-drive space, AutoCAD may simply not have enough room to work. If you have enough or more than enough room (bare minimum is 25% free space of the hard-drives total capacity) then its time to do some work. One of the things I do when setting up AutoCAD (even still), is create a temporary directory directly underneath the AutoCAD install directory called AcadTemp. I direct all temporary files, xref copies, log files, and autosaves to this directory. This eliminates bumping heads with the OS when one or both begin file swapping. So, in your case, you may have a temporary directory filled with err files, sv$ files etc.
[red]*** CAUTION - IF YOUR SYSTEM IS NOT BACKED UP - DO IT NOW! ***
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So what I usually do is reboot the machine, find your temporary directory, and delete any and all files and or folders in this directory. Then (and this is important) reboot the machine again. Once you're back up, do a search for *.bak, *.bk*, *.sv$, *.err, *.dmp and then after determining whether or not you need them, delete these files.
If you have something like Norton Utilities, or Disk Keeper, after you have cleaned these files out, use one of them to optimize your drives. This exercise can take the better part of a day depending on how fragmented your hard drive has become. Best bet might be to start optimizing before you leave for the night and come back to it in the morning. When this is done, reboot the machine again and then start AutoCAD and you should see your plotting performance improve.
If it doesn't, it may be time to reinstall everything from the OS up.
HTH
Todd