My parents have a new Linksys WRT100 RangePlus router at home that replaced an old D-Link. The old router had no problem on my MacBook Pro. This new one would always connect but using any service on the web or even IM would be spotty. Oddly, traceroute and the like showed find transmit times but I think it wasn’t able to push more than one kbps or something paltry like that. It was so painfully slow that I coudn’t even access the router’s configuration page via wireless
After fiddling around hardwired, I disabled the “mixed mode” which is basically B/G/N support and set it to B/G support since my laptop in any case is the only device in the network that supports N. Bingo — back and functional. So, word to the wise: Linksys WRT100 does not love the factory settings on the WRT 100.