button click causing page refresh

[NTSGuru]

I am using a DTC button in my asp which is supposed to grab the selected item in a listbox. the listbox is dynamically populated every time the page is refreshed. my problem is that when I click the button, it refreshes the page BEFORE it executes the code in my button_onclick routine. therefore the listbox always gets set to the first item in the list, and I can't retrieve the value that I want. is there any way to force the page NOT to refresh when the DTC button is clicked?

TIA
Fred