Laptop docking creates video problem

Does this sound familiar to anyone?  SW 2006 runs fineandsnappy on my HP laptop.  But when I use the dockingstation(driving an HP LP2065 monitor) I get the following problem:

I can open three parts, drawings, assemblies, of any size,with noproblem.  When I open a fourth window, the systemgetsincredibly sluggish.  But then if I tile or cascadethewindows, the problem goes away.  

This suggests to me that it's a video card problem buthowdoes that explain the docking discrepancy?  Is theresometwo-way video information flowing through the dockingconnector? I'm stumped.

I'm using an ATI Mobility Radeon X1300 card with 512MB ofmemory.SolidworksAdministration