I have a Linksys WRT54G (ver7) Wireless Router.
I bought an xbox360 last week, and im using wired connection to access xbox live, and now there is no internet on my dad's computer (he use wireless connection). Signal is good, but he can't access the internet.
i will bet your dad's comp is set up to obtain ip address, i would check your "starting ip address" in your router settings to make sure it has enough ip's to issue without duplication
like he said check both ip's to make sure they are not the same, if they are check to see if your dad's is obtained automatically (xbox 360 is by default unless you altered).... if it is then i would check router settings for issued IP's