New Yosemite Macs won't run Snow Leopard even on an external drive. 🙁
Generally the oldest version of OS X that can run on a Mac is the version that it was installed on it, when you bought it.
Ah, I wasn't sure the OP uses a modern Mac. That is a limitation of course, though running SL (or Windows) virtually would work, I guess.
The mouse pointer will color cast correct. And you are practically done.
Clicking on neutral grey parts of the photo is usually the easiest but sometimes it doesn't work because of how the image is.
Another option, which I've recently begun to use quite a bit, is the "Ring around" feature. This presents the image in a 3x3 grid with the current colour in the middle and other versions - akin to the LAB colour space works, it seems - around it. Clicking one of the other versions adds, for instance, a bluer cast to the middle image etc.
The Auto colour feature (I think that is the name) is also useful but works better on C41 than on transparencies. Very often it will be spot on when selected, but if it is not using the slider will always find the right colour balance.
I don't use the film profiles in Color Perfect because they always look unnatural to my eye. The Gold 200 profile, for example, is way too saturated.
My workflow, in brief, is:
1. Scan as linear scan (as described on the CP site)
2. Open resulting TIFF in CS6. Dust spot and crop as necessary. Save digital original.
3. Set colour space to sRGB and open image in ColorPerfect (I know views vary as to whether it is good to use sRGB here).
4. Select correct mode: ColorNeg or ColorPos (I almost never use TouchUp). Then pick L mode (for linear). Sometimes, however, I find that G is better even though I scanned linear. And very often, even if L is better than G, I will not use the colour space sRGB but instead tweak the Gamma setting (usually 1.8).
5. Adjust the Black and White sliders, all depending on the image (very subjective).
6. Adjust colour as outlined above by clicking on something neutral, using the Ring around feature or the auto colour feature.
7. Ok out and continue editing in CS6 as necessary.
br
Philip