Can you ping yahoo.com? If not, what's the error message? And if not, can you ping 66.94.234.13? (Yahoo.com's IP.) What are the ping times?

*idea bunny hops in, looks around, makes a poo, and says, "tell everyone in the house to disconnect, and then test it again. if it's still not connecting, check the settings on your machine itself, and whatever usage stats you can find"*

Agropyron: average time was 109 ms. It doesn't happen with all sites, I'd say 1 out of 3 or 4. I only have one user other than myself connected right now. Haven't quite seen this kind of selective dropping before. Thanks for the poo, amberglow, I'm gonna try that next.

Oh, and I have to keep clicking repeatedly or refreshing in order to eventually get through.

Sounds like more of a time-out issue if you are able to connect sometimes but not others (assuming it is random and not affecting some sites but not others). First, smack the guy downstairs around until he stops sucking the bandwidth up, then try again - that will confirm/eliminate bandwidth as a cause. Second, do what amberglow says, or do an iprenew on all the computers to make sure they get a new IP address (best to do this after turning absolutely everything on the network off to make sure you start with a fresh configuration.

I had exactly this problem when I changed ISPs last week and, after tearing my heair out for several hours, it just went away by itself for no apparent reason - make sure that you do not have caching issues, which I suspect was at least part of the problem for me.

Is it only specific pages that won't load, but others work just fine?

Or is it hit or miss on all pages? Some pages load, and then don't load? If so, it might not be DNS:

Are you out of effective range of the AP?

Are there other networks in the area?

Other networks that might be closer? Stronger?

Are they on the same protocol? (IE, 802.11b, a, or g?)

Are they on the same channel? (Usually channel 6 by default.)

You might need to force the AP and all clients to a different channel. For starters. Each channel can only handle so much signal - and AFAIK that signal is shared across whatever devices are in the footprint on the same channel.

There's even more tweaking you can do with beacon length and frame sizes and whatnot that may or may not be related to this kind optimizing for bandwidth and footprint size, but that's above my at-hand skill level.