you probably need to compact the workgroupfile when no one (including you) has the workgroup file open.
I'd suggest opening a copy of access using another workgroupfile (probably best done as a command line switch /workgroup="newworkgroupfile" - I think thats the correct form but check on the msdn site. or make sure that no other users are using access with that same workgroupfile.
it may make more sense to do the process out of normal working hours, so it could be sensible to inclide it in a batch process, failing that you may have to wokr out of hours to fix it if its an oneoff problem.
I'd rather be riding on the Tiger 800 or the Norton