OK, so here's my latest findings, and fix (for me anyway)
The problem seems to be that the Dell wireless utility clashes over management of the wireless signal. Every time I transfered a large file over the wireless network the network would crash.
By disabling the Dell utility (services.msc, dell wireless, change from automatic to disable) Windows had sole control. Transfers were slightly faster and better still, stable.
So I took a deep breath and uninstalled the Dell utility. One restart later and Windows 7 has installed the driver, but not the utility.
Good points - Totally stable wifi with no drop outs. 7 controls all the adaptor functions.
Bad points - The automatic wifi disable on LAN connect no longer works along with things like afterburner.
However, I can live with that knowing that there is no longer a clash and it's easy enough to turn wifi on and off using F2.
I don't know if this is of any use to anyone, but I just thought that I would let everyone know what I found out.