I'm posting this as Netgear UK have yet to get back to me with regards to the above wireless router and the initial solution they offered actually made the problem worse. Which is possibly why they haven't replied yet.
To cut to the chase when I use MSN messenger I can receive large files over the network from my friends (I'm an animation student so we tend to use MSN to send each other our work in progress - the problem is that I can't send anything over about 1.5/1.8 MB without the transfer fail.
Now I've checked Microsoft's website and can't see anything about a restriction on file sizes with reference to MSN so I'm assuming it's the router. Netgear suggested that I reduce the MUT to 1000 Kb and that this solved the problem - which actually exacerbated it as I couldn't send anything without the transfer failing.
If anyone's got any idea's I'd be really appreciate some advice - I should point out that this happens with all of my macs which are running airport (in various guises) to access the router/internet. And whilst I can put a network together as a non techy routers and firewalls are a bit above my technological expertise