I had a strange situation where my XP guest would login fine to a domain and everything would work for a period of time. Suddenly the CheckPoint client would pop up even though I did not request anything in the Guest. After this none of my mapped drives would work any more. I suspected that the issue was linked to the CheckPoint client in XP but it actually is because I connected the CheckPoint SNX client in the host GNU/Linux system.
Once the SNX (on the host) makes a connection, new network routing information is available along with new nameserver entries in the DNS /etc/resolv.conf file. After a time this gets passed through to the Guest OS despite the fact that the Guest is running in Bridged mode and should be taking care of this itself. The XP guest picks up the DNS entries for a network that is behind a VPN so it prompts for a connection. If it isn’t made, then it fails and doesn’t look any further. As the network drives are mapped using a DNS name then they are no longer resolvable.
I’ll probably want to look into a better solution than this but for now remove the dns entries from the /etc/resolv.conf and run ipconfig /renew within XP.