Getting wireless up and running in gentoo is very easy refer to http://gentoo-wiki.com/HARDWARE_rt2500 

for a detailed explanation.

In summary this is all what you need to do

1.emerge wireless-tools
2. since my card is RaLink RT2500 802.11g Cardbus/mini-PCI i refered to the above http://gentoo-wiki.com/HARDWARE_rt2500