WinVista GPO log on Script odd behavior

Testing Environment: Virtual Server 2k5 R2 hosted on Win2k3 Ent x64 Ed.
Testing Environment LAN: Local NAT bound to MS loopback adapter with WAN
access via ICS

Virtual OS Instances:

Win2K Server: Virtual AD PDC.
WinXP: Client Machine
WinVista: Client Machine

GPO Log On Script:
Language:VBS.
Purpose: Map Three Network Drives (X,Y,Z)
located on PDC

Problem: When logging onto the WinVista instance with an AD account that is
a member of Either the local Admin Group or local Power Users group (test
account is a member of one or the other never both) the VBS logon script
fails to acctually mount the network shares. I have verified that the script
is running by inserting a couple wscript.echo statements before and after the
wscript.mapnetworkdrive statements, the wscript.echo's come up as expected
but no network drives. If I remove the AD account from the local Admin or
Power Users Group the drives map perfectly upon next log on. If I perform
the exact same test on the XP instance (ie add the testing account to either
Local Admin or Power Users) drives map perfectly in both cases.

Any Ideas