I'd have to guess with a:
If you look at your fstab entries for your windoze partitions, is Supermount involved at all? If not, are the drives mounting at boot time, or is it only upon access to them? I suspect basically that the drives aren't getting loaded until you attempt an access on them. This would explain the sluggish-ness you are describing. To remedy that you could edit the fstab entries surrounding your windoze partitions to your exacting needs and have it get mounted during that AMAZINGLY long boot time
(The ONLY gripe I've had with Mandrake since 8.0 was the boot time).