If you wish to have the local (WLAN) PCs able to view the intranet pages, you'll need to first assign the hosting/serving PC with a static IP address in the router's config (for example
http://192.168.0.2).
Then your local PCs will be able to browse to that address (or else \\PC-Name) to see the content. If you're asking about serving pages WAN-side (to the internet) then I'd advise you connect the hosting/serving PC to the router via ethernet; in fact you should do that anyway. You will then need to set a static IP (as for local serving) and open port 80 on the router and forward it to that static IP. You'll only need to do this if you're serving pages to the internet (WAN) not the intranet (LAN/WLAN), and only then if it's a "normal" machine. If it's a dedicated server you may as well stick it in the DMZ.
If you have a domain and the PC is serving the internet (WAN), your local (LAN/WLAN) PCs won't be able to resolve that domain unless your router has NAT loopback, so don't let that catch you out into thinking the PC isn't serving pages...been there, done that!
By the sounds of it though you're simply wanting to host a page/site on your local network (an 'intranet') for the other PCs in your house to view. In which case it doesn't matter whether you're on wifi or ethernet, though the latter is preferable. In either case the setup is the same, as detailed above.
I'm sure someone will be along soon to tell you how wrong I am, but that's how I do it. Oh, except I run Apache for the proverbial win.
EDIT: Damn you sp00n and your l33t non-waffling skillz.