Can access VPN but unable to see Servers

I recently upgraded to snow leopard on my macbook. I used to be able to access my works servers via vpn/ RDC prior to upgrade, but since moving from OSX 10.5.8 to OSX 10.6.4 I have not been able to access the servers. As far as I can see, all settings are the same. I can ping the VPN address, but nothing else. I have another laptop with older OS which can still see the servers. Can anyone tell me what has changed? Is it something I can fix my end, or do my IT admin need to change something?