Okay, so after some tinkering with my tablet on GIMP I found out two things.
1. Short, quick brushstrokes work just fine with no pixelation. So if your art only needs that kind of paint action then you should be fine.
2. BUT if you happen to want to trace a scanned work with long lines across the screen then you're out of luck. You will get pixelation no matter what. If you want to trace something scanned that you've already drawn then I'd have to recommend vector lines to do it.
Just got a Wacom Pen Tablet and I'm having the same problem. I'm using Gimp & Corel Painter Essentials programs. I get a jagged fuzzy line each time. I've tried a resolution around 300dpi and the problem still persists. I'd like to mention that my tablet feels too sensitive almost to the point where I can't even draw a nice square! Anyone know how to tweak this? I'm running out of options, I might have to just settle for overly meticulous vector art, ugh...
Is this your first tablet? 'Cause all lines on all programs with all tablets tend to be very jagged. They're very... touchy. You can get around this relatively easily by upping the resolution on the pictures that you use, or by editing the correction of the pen on the pen menu.
Are you sure you have anti-aliasing on? If not, the lines will be jagged and hard pixel edged.
I had a problem at one point that required me to delete the configuration profile, or something like that, and it fixed my jaggedness problem.(but this had to do with me drawing, and the line being jagged, then fixing itself once I picked up my pen)
Well, when you're in photoshop go to the paintbrush/pencil, make sure it's set on brush. If it's set on pencil, then it will not have anti-alias. Then you can set how much anti-alias you want by clicking on the brush shape picture and changing the hardness.
The way the program is set up should be the same for both macs and pcs.