Oddly enough, the system (after maybe 5 months of this habit) seems to have miraculously improved itself. The only change I made was, from the Mac side, Virtual Machine -> Settings -> Hard Disk (SCSI) -> Advanced Options -> Pre-allocate disk space. I have a 100GB virtual HD split into 2 partitions (40 and 60 GB). XP lives on the 40GB side. Normally, I only hade "Split into 2GB files" checked, so I checked the Pre-allocate option as well. My Bus type is SCSI.
I don't think I touched anything else on the Mac or Windows side after that. The pre-allocation took some time, but after I rebooted, it "appears" to be working as it normally would.
Best,
Michael