Here is what I did I have a R580 with an i5 and 310M nVidiA Card. Download the 10.6.5 combo update and everything else you need before hand (on external drive or thumb or even a DVD) to have after you install SL. using iBoot+MultiBeat. Run the 10.6.5 update, and then run multibeast (only check this ONE option=EasyBeast when you run the program the first time)........This might kill the trackpad (after u restart)...., just reinstall the keyboard and trackpad kext(s) with a usb mouse and keyboard if necessary...... Run MultiBeast again (before you restart) and install the programs it comes with to install kext, which is kext helper b7. Use kext helper b7 to install the kexts i'm using to S/L/E folder (which is the only location it will install to, for the Extra/Extensions folder you can drag and drop as long as u use kext utility afterwords). Then everything should be good, restart and then use software update (click the apple in the upper left status bar) and download and install only the 10.6.6 update . After you install 10.6.6 u can use software update to update other things if you like. Here are the kexts Im using but I'm using a DSDT so Just click easybeast only in multiBeast. And add the kext I have in your System/Library/Extensions folder using kext helper or kext beast EDITED: One of these is in MultiBeast but wait until after you install EasyBeast option from MultiBeast, don't restart yet...install the programs from multibeast and then install the kexts before you restart.
System/Library/Extensions