I was afraid you'd say that. Version 8 of the WRT54G is a crippled version of the hardware. They reduced the RAM and Flash area by 1/2 of the previous models. This doesn't allow you to run 3rd party firmware, which typically runs much faster.
Make sure that logging is turned off in the router (default setting anyways). Set your wireless to G only, and give both sides a good power cycle. Start with turning off the router, leave that off, then turn off your cable/dsl modem. Wait a minute or two, and then turn on the cable modem. Wait for that to fully initialize, then boot the router up.
Next, clear your cache on your browsers and try again. Or, if you are still within your return policy time, get a WRT54GL (linux version), and you can have many choices of 3rd party firmware, or even stay with the latest Linksys version which is now very stable and fast.