last year when I was on a laptop instead of an iMac I did sometimes got unexpected results from using the trackpad. Even on my laptop I ended up hooking up a mouse for Vue6. Maybe just get a 2 button mouse and try that first if you arent keen to upgrade?
I only upgraded 3 months ago to 10.5... have to say I really do like Leopard after avoiding the upgrade for sometime.
Photoshop CS4 doesn't always play nice with it and you might remember my Hex problems from a while back - Hex an 10.5 are a total no go! in my book.
Works great with Vue7 Complete though.

" Try and be nice to people, avoid eating fat, read a good book every now and then, get some walking in, and try and live together in peace and harmony with people of all creeds and nations."
-Monty Python