Hey, Craig... Welcome to
RP.
Lonnie provides sage advice. Photo Impact is a very capable program and you're used to using it. For the time being and for your particular needs, PI should serve you well.
Switching to another program would be like moving into a new house with a completely furnished/stocked kitchen you've never used before and given the task of whipping up dinner while blind folded -- or at least one eye covered and one hand tied behind your back. Sure you would eventually be able to serve steak, potatoes, salad & desert, but in doing so would be faced with many occurances of, "Where's the darn [whatever]" and "How do I do [whatever]." You'd be able to deliver the same result faster from your own kitchen with little or no loss in quality/tastiness.
As one with considerable photography background you know the main task is to get the photo right. Doing that = little post processing work: A little sharpening, tweak saturation and/or contrat a bit. Crop and print. It's more "the photographer" (knowledge, experience) than the camera used that is instrumental in getting a great pic, esp. of challenging [moving] subjects like dogs.
If you haven't yet... Google something like:
pet photography
...to get some ideas on how others have approached this business.
Also check out:
http://www.pbase.com/isabel95
Isabel has done quite a bit of pet photography.
Good luck as you move forward with your endeavor. Keep us posted as you make progress.
Sure, Photoshop CS3 is now the big dog on the block, but do you need an SUV when a minivan will do?