Thanks - there are loads of great links there ...
Now I am back using a wired LAN

.
I really don't know what gives with my WiFi card - my system seems to run fine so long as I don't try and access the internet via WiFi !!!
I reinstalled my Corsair RAM and tweaked all the BIOS settings to the recommended settings and I still get memory errors - now I have sent it back for a replacement! I ran MEMTEST86+ overnight on my older Crucial PC2700 and get no errors at all.
I ran Prime95 Torture test for 3 hours this morning - no problems at all.
Tried to look at a webpage and crash!
It's really frustrating as it seemed to be sorted for a couple of days. I reinstalled windows but I am still getting the same crashes and I notice that even on a fresh install the NetGear app keeps popping up the TaskManager list with brief 16-20% CPU usage even when the system is idle. All very strange - I can only presume there is a driver clash somewhere but there are no conflicts in the device manager and it is running on an IRQ on its own.
The only other problem that I can see is if there is a PCI problem - but my Audigy sound card and HaupPauage TV card both work fine.
Any ideas how to troubleshoot this? I have emailed NetGear and posted a request at ASUS forums so we shall see what happens. (NetGear email tends to be pretty slow and unhelpful).