MBP and Snow Leopard issues

[BasilFawlty]

I bought a new MBP with Lion, but have SL installed on a external disk because I have some apps that won't run on Lion. However, when I boot to SL, my track pad doesn't work completely. For example, on a web page in Safari, it won't scroll using the finger motions on the track pad. When I look in Preferences while running SL, and select track pad, it says it's "searching for bluetooth trackpad" and doesn't seem to recognize the built in track pad.
Is the MBP made to only work with Lion, or is there some setting somewhere that will address this issue. Has anyone else had this problem running SL on a newer MBP?

 

[salacious]

and why would you run a OS on an external drive?

 

[BasilFawlty]

and why would you run a OS on an external drive?

I have my reasons. Still hoping someone can help.

 

[Mojo1]

If the MBP isn't compatible with Snow Lion it won't even boot. I suspect a driver problem. Try a Google search and see if you get any forum hits about similar problems.

I don't see any problem with booting from an external Firewire drive. I've done it plenty of times. It's a simple way to be able to use legacy programs with a newer Mac.