Its pretty easy to set up a secure wireless connection. Just type in the IP address of your router and go to wireless settings and then go to wireless security. Then select the type of security you want to use (WEP, WPA, WPA2, etc.) I would recommend WPA-PSK or WPA2-PSK, since WEP is easily breakable PSK stands for Preshared key (a password or passphrase) . Now just chose a password and remember that or write that on a piece of paper and click apply. Then you'll be disconnected from that network so just click on the airport menu and select your network and then input your password. You can do the same thing for your other router and the password does not have to be the same. OSX can remember the security settings for many different networks.
My linksys router WRT54G may be different than yours but to get the general idea heres a screenshot