Yea.. u prolly right, but i've googled this for quite many hours.. Might be that i lack brain to find correct searchwords though
But.. the good news is that i managed to work it out..
Solution :
using OnChange() event on the "Postnr" field, which triggers a function with an IFRAME (which is _not_ a popup), with "postnr" as parameter.
Using Request.GetParameter("postnr") and put it in a temp variable.
Then i build the SQL query with the temp variable and picks out the Postnr, followed by putting the value into a hidden field on the "IFRAME" form.
End it all with sending the value to the parent form and closing the window..
Voila..