Thanks for everyone's advice. I tried following a set of instructions specifically for my router (it's a Netgear MR814) - but I was altering settings on my Macbook Pro, which is not the computer that the router is connected to. I realised half-way through that that seemed a bit stupid. Should I be doing the altering on the computer that is connected to the router? I'm a bit confused. I tried to set up a static IP address as instructed, but on my MBP, and when I did it, I could no longer connect to the internet. Tried to change it back to the way the settings were originally and it told me that Airport was connected to my wireless network but that it didn't have an IP address and therefore couldn't connect to the internet. It took me a surprisingly long time to figure out that all I had to do was run the Airport setup assistant to get back online, so had a bit of a panic there. I did have a read through some of the introductory material on forwarding ports, etc, but to be honest I find it all a little confusing. The computer that I have my router connected to is an old iMac running OS 9. Should I be changing the settings on that, and would it work the same way with OS 9?
Thanks again!