My laptop has the Atheros AR5005G chipset, which works great with
MadWifi, just had to doubleclick the RPM file and everything was working after a restart.
I also have the ASUS WL-107G PCMCIA card that uses the rt2500 chipset and it was working great on my previous laptop.
I have to mention I have neither tried WEP nor WPA encryption because the networks I logged on to (Uni & restaurants/bars) were open, so I don't have any experience in that respect.