Nick - I have photoshop but using layers does my brain in!
I think I need to really sit down and use a proper tutorial because by the looks of it I could most definately do what I need to do in photoshop - rotating each of the 3 images (removing field rotation) and combining the 3 images. Sometimes I feel like a complete novice while using photoshop
Fahim - thanks for the alternate software suggestions. I downloaded and tried stellar magic, at the price of *free* it is in my price range
It does the RGB stack and align very well, however it doesn't remove field rotation so I would have to figure out how to do that manually if I use that software.
I think my best bet is getting to know layers in photoshop in depth, I just need to invest some time in learning it all!