I get the pattern with no apps running. However, I have Airlink101 Cardbus and PCI Wireless LAN Utility running on StartUp to connect to the household wireless network. The connection doesn't seem to work properly, so I shut off the Utility to see what would happen and, of course I have no wireless connection but, I have no more wildy chaotic pattern. So the Wireless Utility seems to be the culprit... (likely).
If I use the other OS (dual boot) then this utility need never run. I guess the only question now is how much space does an old version of Windows XP sp3 need on the HDD? Can I get away with 10 GB if I'm not using it anyway?