Massive Slow Downs.....

We have a farm of 7 machines, Dell 2450's W2k SP2 XPe
FR#1. Applications are no more exotic than Office 2000
and one or two home grown apps. We are using Lotus Notes
5.11 and have been running this config since TSE 4.0 and
Citrix 1.8. However 8 weeks ago we added ACT! to our
Notes server and ever since that day we have had these
periodic slow downs. The server will drop to a
standstill, users will not able to do much of anything
for 3 to 5 minutes then it snaps back to life. This
happens via RDP and ICA. I have not been able to get a
perfmon yet but taskmanager shows the CPU at a near idle
when this occurs. We are publishing desktops and
redirecting the Desktop folder, startmenu folder and the
My Doc's folder to a DFS share. The DFS server never
experiences any performance problems......

We have disabled the virus scan software (McAfee version
7.0) to no avail.

I am at a loss for words.