WileyCoyote,
It is possible that Windows (either XP or Vista) were not able to resolve a network connection before starting up (happens to me all the time). The questions I need you to answer are:
1. Do the connections eventually establish?
2. Are the network drive connections mapped by IP address? (if not then refer here for support on mapping via IP)
If the drives are mapped via IP address your computer is able to resolve the connections much faster when they first start up than when mapped by the NAS network name. I hope you find this information helpful.