Yeah, VPC Additions is what I meant.
As for the error... urg... I've never seen that before. I'm not using XP; just Win2K, but even when I did put XP on just to see what its performance was like, the Additions installed just fine.
Looking at my real winxp machine, if you open the Disk properties in hardware manager, there's a tab for "Policies" where you can turn off write-back caching:
Turning this off will certainly cause a performance hit, but it may allow you to get the VPC Additions installed. You could then turn it back on once they're installed, but if you keep seeing this message, I'd be a bit concerned about the integrity of data within the VPC volume.
Are you running FAT32 or NTFS within VPC? FWIW, the XP install I did was with NTFS, and I did not turn off writeback caching. Also, is this a fixed-size or dynamic VPC image (mine is dynamic)? Don't know why that would make a difference though...
Hope that this helps...