getting aux display on laptop to be the only display

Tue Jun 9 00:09:20 UTC 2009

I have following hardware on my laptop:

 > dmesg|grep vga
vgapci0: <VGA-compatible display> port 0x6110-0x6117 mem 
0x90000000-0x903fffff,0x80000000-0x8fffffff irq 16 at device 2.0 on pci0
agp0: <Intel GM45 SVGA controller> on vgapci0
vgapci1: <VGA-compatible display> mem 0x94500000-0x945fffff at device 
2.1 on pci0
vga0: <Generic ISA VGA> at port 0x3c0-0x3df iomem 0xa0000-0xbffff on isa0
drm0: <Mobile Intel\M-B\M-. GM45 Express Chipset> on vgapci0
vgapci0: child drm0 requested pci_enable_busmaster

and I have an extrtnal 21" widescreen (vga) that when I hook it up the 
default x11.config  has it  at  1024x768 on *BOTH*  monitors.... How do 
I make it so X only considers the external (if attached) monitor?