Problems w/ internet access wirelessly

Hey there.
We had a wireless router that was giving really poor signal strength to the upstairs. So I pulled out the old router and set it up. It gives my Macbook great signal strength upstairs but I cannot get allowed INTERNET access. I can ping the router with no packet loss.

I have 2 Windows directly wired to the router and one wireless Windows - all of wich have internet access.

Router info:
SMC Barricade G
SMC2804WBRP-G

Mac info:
OS X 10.4.11 (Tiger I believe this is? Im not exactly familiar with the feline species that my OS is yet...).


Thanks;