it probably already is enabled. right click your desktop, click nvidia display, click performance and quality settings, select the application (oblivion in this case) then look at all the settings for it and SLI is in there. like i said, it is already enabled if you haven't touched it before.
[CPU: e6600 @ 3300 MHz] // [MB: ASUS P5N-E SLi] // [RAM: Patriot 'eased latency' PC2-6400 @ DDR800 5-4-4-12-2T] // [GPU: 8800GTX @ 650/1000/1600 (volt modded)] // [HDD: 2x Cavier 500GiB stripe] // [Chassis: Thermaltake Armor VA8000 (black)] // [PSU: Aspire(Apevia) 680w] // [OS: Windows 7 Ultimate x64][Cooling: water cooled GPU and CPU]
^ (9/7/2010): Ha, I remember when that was the stuff. My water cooling has since leaked and fried my mobo. So now I'm rocking an MSI laptop with an i5 430m :)