Vista drops shared folders during reboot

First machine is a PC with XP, second is a laptop with Vista. I've
created shared folders on the PC (XP) that I can access on the laptop
(Vista). However I cannot get a shared folder on the Vista machine to
survive a reboot. If I quickly open the "Computer" as the start-up
programs are loading (widgets, anti-virus, etc.) I can see the share,
but just as the laptop connects to the wireless network the little
shared icon disappears and the folder is once again unshared.
Laptop is an Acer Aspire 5610.
Any ideas?
Thanks.