I've always had this problem, and as a result I really can't use an external mouse with OSX. I've never had a problem with using the trackpads.
Like one of the commenters mentioned, using synergy from a Linux PC solves the problem for me. For a period, I actually resorted to running a Parallels instance of Linux with the external mouse attached to it, and setting up synergy to share the mouse pointer with OSX.
I'd like to run Linux as the main OS on my MacBook Pro, but in Linux the problem is the opposite: I've never found any driver / setting that makes the touchpad work really well under Linux (any hints would be appreciated - of course, I could always run OSX in VirtualBox under Linux, connect the touchpad to OSX and share it using synergy.... :)
Yeah, that's the one reason I never really run Ubuntu on my Air, even after I successfully jumped through all the hoops to get it installed. :)
I tried several different sets of tweaks but none of them felt right. Especially, I don't think any of them let you select with one finger and then drag with a second.
That's one of the things that the fairly recent Multitouch patches to the Xorg input layer should begin to fix. How long it'll take for environments to start implementing things like that I'm not sure.
Touchpad support in Linux is a crapshoot and the uni-button, multitouch touchpads are even worse. If you poke around the Ubuntu forums there is a rewrite of the touchpad driver that works better for Macs. Then you just have to deal with the atrocious battery life compared to OS X (though that has to do with MBP's lovely implementation of EFI and the graphics switching).
Like one of the commenters mentioned, using synergy from a Linux PC solves the problem for me. For a period, I actually resorted to running a Parallels instance of Linux with the external mouse attached to it, and setting up synergy to share the mouse pointer with OSX.
I'd like to run Linux as the main OS on my MacBook Pro, but in Linux the problem is the opposite: I've never found any driver / setting that makes the touchpad work really well under Linux (any hints would be appreciated - of course, I could always run OSX in VirtualBox under Linux, connect the touchpad to OSX and share it using synergy.... :)