How to Network Laptop (with Vista) to Desktop with XP

I have a new laptop (Dell with Wi Fi) that has vista premium on it and I want
to be able to network the laptop with the Desktop so I can access files that
are on my desktop. I have already set up a Network (is this what you call
it?) so that I can get onthe internet on the laptop using the Wi Fi (My Modem
/ Router that is conected to the desktop by ethernet allows wireless - not
sure if this makes sense? Im not good at all the terminology). Anyway, what
I need to do is be able to access the files onthe desktop via my laptop - can
someone tell what I need to do now? Do I use the same network that I already
have set up (the one how I can get on the internet) - or is this network I
have set up (and is working just fine) only to be able to get on the net and
not to be able to access my desktop computers files? I have played with the
Network and Sharing centre but cant seem to get my head around it all. I
have named the laptop and the desktop and have given them the same name for
the workgroup name. But now I dont know how to get them to talk to eachother
- can I do this with the Wi Fi? or do I need to plug in a cord from the
laptop to the desktop?

Confused!