IE 7.0, how to do postback inside a modal popup

[tete]

Hi there,

i have an app that opens a modal pop-up and inside of it i need to do some
postbacks at my controls.

At IE 6.0 everything runs fine (i use the tag base=xxxx at the HTML).

But at IE 7.0 it opens another windows everytime it's do a postback.

What could be happening?

Thanks in adv.
Fabiano