I know it's late/early (at least in the UK) and no offence intended, but please read my original post which does state ;
No other PCI cards are present when the installation is attempted
I agree - I thought it was an IRQ conflict. Everything possible/unused I.e. serial ports, parallel port, onboard sound has been disabled in BIOS. The BIOS on this particular PC does report IRQ conflict on bootup if there is one - this is not being reported in this case.
As for memory conflict - I don't have much of a clue where to start looking at that to be perfectly honest.
I have had one constructive suggestion - go USB. That would at least allow me to stick with the Netgear and the RangeMax feature. I did originally want to go Linksys but neither retailers that I use could provide the whole kit. With it being wireless I insisted that all the kit was from the same manufacturer.