Here's a quick sample I whipped up. Basically, the dialogbox only acts if id 1 (the Yes button) is pressed, otherwise the dialogbox stays active. I basically took one of the sample scripts and added a second pushbutton. Hope this is what you were looking for!
proc main
integer Event ; Dialog box event.
dialogbox 0 8 20 257 92 2 "Completed?"
pushbutton 1 35 39 40 13 "&Yes"
pushbutton 2 182 39 40 13 "&No"
enddialog
while 1
dlgevent 0 Event ; Get dialog event.
switch Event ; Evaluate dialog event.
case 1 ; Button was pressed.
exitwhile ; Exit the while loop.
endcase
endswitch
endwhile
dlgdestroy 0 CANCEL ; Get rid of dialog box.
pwexit
endproc aspect@aspectscripting.com