wifi problems - i don't know what to do

a few months ago, i started having this issue on my MBP with 10.5 where airport would show it was receiving a signal, but i would not be connected to the internet. when i click on the airport icon in the menubar (fully black), it usually says "scanning". my network as WEP encryption, however, it often shows that there is no password and i have to enter it in again, about 70% of the time i wake the computer from sleep. if this "scanning" problem occurs, i often have to go into "join other network" and enter my SSID and WEP code again, every time i want to use the internet. but then a lot of times that still doesn't fix it. the only way to get it to work in those situations is to either turn off encryption (or turn it back on if its already off) or change the password. basically, just change a setting, and type the network information back in and it works. i have 2 other Dell laptops on this network, and they are not experiencing any of these issues. when i first got a mac, i was amazed at how simple the wifi was to set up compared to PCs. not anymore. what can i do? i dont know of any troubleshooting stuff i can do? also, it takes about 15 seconds to connect to the airport after i wake my mac (when it does connect), when in Tiger it took about 2 seconds.... i thought 10.5.2 or the airport update was supposed to fix all these wifi issues?