for linksys you can access it via your browser. use 192.168.1.1 then after you've entered the setup password you can enter the setup menu. you can now set wireless security using either wpa or wep or whatever protocol you have. save settings after
WEP is still better than no encryption though. Usually, upgradeable naman ang firmware ng mga wireless routers and cards, so if WPA support is not there, just check the vendor's website for updated drivers.