I'm still having problems and I dont know what to do next.
I formatted the machine last night. I now have a completely clean, new Windows installation. I've installed absolutely nothing bar the drivers for my Linksys Wireless card, and the Realtek Audio drivers along with chipset and video drivers. Thats it. There is nothing else at all on the system.
Whilst I've not had a BSOD, I'm getting truely bizarre internet performance. At times it's like being on a saturated 56k modem link - you load a page and half of it loads but the rest takes an AGE to appear. You click a link, it sits there thinking about it for literally 3-4 minutes before actually loading. Half the time I expect it to time out. Sometimes it actually does. Sometimes, however, it's perfect, and like lightning.
All this would point to problems with my network but sitting right on the desk next to my keyboard is my laptop - and this works absolutely perfectly. I've even done tests when the problem happens.
For example, just now, I loaded the OcUK forums and clicked General Discussion. In the time taken to actually load the GD forums, I was able to load the forums, click GD, and read 3-4 threads on the Laptop. They are both connected to the same wireless network, infact the Laptop is further from the router (by perhaps 20cm but you get the point).
It just seems like odd things are happening to PCI devices on my PC and I'm not sure where to troubleshoot from here.