Help Enabling SLI

I have been playing on an 8800 GT for a few days, (PNY XLR8 Edition) and i decided to buy a second one. My comp dual boots xp and vista, so i decided to try XP first. When I got into XP, it said it installed my card. But when i went into control panel, i found NO option to enable SLI. So i thought. OK, thats bad... so i went to Vista, FOUND the option after it installed my card. and when i click Enable and Apply, my screen flashes with the black screen and the blinky line, but the graphics settings go back to default, and Vista says the program crashed, and by all accounts is no longer installed in any way shape or form...

Any insight on how to fix this problem?

Q6600
2gb Corsair Ram
Ultra 600W SLI ready supply
2 x 8800GT


UPDATE-----

SLI now enables in XP. god only knows how it worked, but it DID, and a LOT better than vista did.

Not sure what drivers you are using, but step one is to download the latest drivers so you are ready to install them. Forget the drivers on the CD-rom. Once you have the latest drivers saved to a location you can find (or if you already had the latest drivers), go on to next step...

With both cards installed, uninstall the nvidia display drivers from control panels add/remove programs. Reboot, cancel out of windows searching/ lnstalling the drivers. Then reinstall the latest drivers while both cards are in th machine and the SLI bridge connector in place.

same happens on my comp!
i have xp and vista, cards work fine on xp but when i come to enable on vista
screen goes blank with a flashing line top left?

i have searched the net and done just about every thing and still no joy.

nvidia control panel says the the two cards are there and it works fine untill
i go to enable sli then i get the sum programs need to be shut down to enable
sli click ok and the screen goes blank with the flashing white line.

then have to uninstall the drivers, re boot, and install again,

think i will dump me 2 X 8500gt 1g cards and get a single 8800gt

seem i dropt a clanger getting them in the first place,must people on the net
say your better with one high end card than two mid range cards in sli.