u can pass a variable to the other page using the link
location="newpage.htm?variableuneedtopasson"
then in the newpage.htm read it like so
var passed = location.search
hope that helps to see an example look at 
http://www.geocities.com/unuclan/cobweb
click on the p and g link in the top left and u can see an example. the 
variable is the page that needs to be loaded into the bottom frame. the 
code that gets the variable is in the top frame.
hope that helps it took me a while to figure that one out myself

Chris