Windows clients extremely slow when accessing local server

Hi

I have a problem with the clients at site B, first I will shortly describe
the situation.

Setup:
A Windows 2000 server was at first installed in site A (both geographically
and in the site configuration) this is acting as the "primary"
domaincontroller.
This server is GC, DDNS, DHCP, WINS, Print and file server.

Then at site B there is a windows 2003 server. This is acting as a GC, DDNS,
WINS, file and print server.

The sites are connected through a VPN tunnel with cisco pix firewalls. The
internetconnection is at site A a dedicated connection and at site B a ADSL
1Mbit connection.

The problem:
When the connection between the two sites is terminated the clients at site
B becomes extreamly slow to logon and even to access the local server at site
B. The clients only have mappings to shares on the server at site B. When I
check the clients uses site Bs server as logonserver. But the group policy
seems to be picked up from site A:s server, So I dont know if that could slow
down the file access to the local server at site B...

Help would grately be appreciated.

Best Regards
Perra