Honestly, a capacitive stylus isn't very precise and it doesn't track very well (long lines as in sketching are often broken). I'd consider a tablet with a dual digitizer that comes with a pen like the Lenovo ThinkPad Android tablet, HTC Jetstream, Motorola Droid XYBoard or HTC Flyer (if you can find a Flyer). The Asus Eee Pad Slate Windows slate is great for digital pen use as is the Samsung Series 7 Slate we reviewed.
Windows is a good choice if you need to run Windows apps. If you don't need that, then Android is a good candidate.