We needed a new WAP so I decided to buy a router instead, which was cheaper and I was told has better hardware than a WAP54G, but could do the same job (and more so).

Problem is, I can't seem to configure it to work as a WAP? I thought I would have just been able to plug it in to one of the 4 switch ports, connect to the address (which I managed to do) and configure the IP statically to our network. This doesn't work, and plugging it into our network doesn't return a ping (can plug the router into a laptop and set the laptop to the same IP range though, and this works fine, which is how I configured it to the stage we're at now).

I'm concerned the subnet is related - our subnet is but the router only allows you to choose a pre-configured subnets, of which our one doesn't show. Is there another way to do this? Short of installing DD-WRT (bit wary of this incase we brick the router), I was hoping it would just be similar to using the WAP - so much for saving 10!