Why is attached code so slow?

well, i have no idea why it would be as slow as you describe, but as for the disappearing:
When i use types i dont do it like this:
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
For bullet = Each bulletdata
For alien = Each aliendata
If ImagesOverlap(bullets,bullet\xpos,bullet\ypos,Aliens,Alien\xpos,Alien\ypos) Then
PlaySound Alienhit
score = score + 1000
Delete Alien
EndIf
Next
Next
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
instead, i do this:
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
For bullet.bulletdata = Each bulletdata
For alien.aliendata = Each aliendata
If ImagesOverlap(bullets,bullet\xpos,bullet\ypos,Aliens,Alien\xpos,Alien\ypos) Then
PlaySound Alienhit
score = score + 1000
Delete alien.aliendata
EndIf
Next
Next
]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]
and well, things work.... IF thats a problem...

sorry if im not helping, but i try..