Ooh, fantastic coloring and nice pink hues you have going on here! I like the poses and attention to anatomy especially. I'm a Photoshop user myself but if these kinds of results are possible with SAI I might just be tempted to look into getting it
You *might* be able to get the same effect on Photoshop now, that is, if you have the most recent version CS5. I saw that they added some color mixing features which were non-existent before. I haven't tried it myself since I don't have access to CS5 but try it out if you do!
Before you go out for it, actually, there's an open source tool called MyPaint that's essentially a free version of Painter. You might want to give that one a whirl first and see if you like it. It's also less of a resource hog on your computer than Photoshop is. Look through my recent deviation submissions. They were all made with MyPaint. If you like how they look, follow this link for more info about MyPaint [link] then go here for download [link]