I've now got fed up with this problem. I've tried the swapping my current NIC (Netgear WG311v3) for the one in my old computer (WG311v2) but found that drivers are not available for Vista for it.

I'm going to buy a new NIC but I'm a bit confused as to what I need, should the cheapest one be alright? Or is there a noticable difference between them? I think I'll avoid Netgear just in case my computer is having a tantrum with all Netgear cards rather than just this one.

Well, it depends largely on how you plan to connect to your network.

If you're planning to use your machine wired, then even the cheapest wired Ethernet cards will work just fine (make sure it's at least Fast Ethernet [100BASE-TX] though. That said, most are Gigabit Ethernet [1000BASE-T] these days). I've had a variety from expensive to cheap cards, and they all achived the same task very well indeed - there's little noticable difference over a simple, small, UTP-wired (e.g. Cat5) LAN.

If you're going wireless, you have more factors to consider, including things like propagation loss from your wireless router, and any possible interference or slow fading. For this, I'd advise checking out some reviews of wireless cards - as the given specs often mean very little in terms of outright performance in a home environment. You'll probably want to go with something more reliably branded for something like this. Belkin cards are solid enough (nothing particularly special), so are Netgear - and a variety of others. Just check some reviews out.