In your (square pixel) graphic application use for NTSC 720 x 534 pixels (4:3) and 960 x 534 pixels (16:9 anamorphic), for PAL (Square pixel apps.) use 768 x 576 (4:3) or 1024 x 576 (16:9 anamorphic).
Photoshop (CS and up) has template from which you can work (also pixel aspect correction, very handy)
John Twigt
Workstation BV, Amsterdam
The Netherlands
http://www.workstation.nl