The new GIMP for Mac reads pressure sensitivity, I just need to mess around with brush settings. For others who search the forums for a problem like this: GIMP for Mac is free and as I've used GIMP extensively in the past I recommend it for your drawing needs. When using it for Mac though you may need to go into your Input Device settings under GIMP's Preferences and set the Pressure curves to Screen or Window, and then adjust the curve on the graph that pops up in the window.
Fire Alpaca is a nifty, simple little freeware, I just got done fiddling with it. Compared to GIMP, it lacks about 80% of the tools and has no filters, but its pressure and pen motion reading is very smooth. It also has a set of Snaps, from Grid-based snapping to Vanish Point. Fast and smooth, good for sketching and doodling pre-op pages and pieces.
I also just tried out photoshoponlinefree.com, which is a slimmed-down browser-based Photoshop alternative. Obviously not nearly as powerful as Shop itself, but a nice alternative if you can't get programs to work on your computer.
Also of course there is dA's own Muro appliction, which I had tried using before posting this thread. It's alright, but I found the free online Photoshop to be better. Muro is prone to lag, as it records every motion you make.
I was gifted ArtRage (thankyouthankyou ;w; ); it's taking me a bit to get used to a more "realistic" approach, as ArtRage mimics actual paints, pens, crayons and airbrushes and has drying times and such. A fun program to mess around with, I'll probably be getting more seriously into it later. The free version is limited of course but has more options than most trialwares, another recommended art program.
--PaintTool SAI is not made for Mac. There is a Wine-skinned version for Mac, but apparently it's not very reliable and cannot read tablet input.
Adobe got me my serial number, thankfully, but I can't reinstall Photoshoop because my CD drive is totally gone now. It hung on just long enough for the reinstall of my OS, but now it won't read anything :'c On the subject of Adobe though, there's a lot of buzz about them offering CS2 for free. Technically it's free. However, it's only meant as an archival for users who had already purchased a CS2 license. Even though it's publicly offered, it's not meant for free download. While I would take this chance, I dare not, as my dealings with Adobe in the past have shown colors I'd rather not get involved with. Seeing how money-hungry they are, they could easily file lawsuits against those who "illegally" downloaded and registered these CS2 programs. While I doubt they will since they were stupid enough to leave it in public access, it's a chance I'd rather not take.