• Why do some people recommend 640x480 and some 720x540?
  
• I thought NTSC video is 525 scan lines. What is this "486" and
  where does the "720" come from?
  

Placing One Video Format Into Another
Video Source	Change: (What does this mean?)	Image Example
4:3 to 16:9 Full-Screen	Height 133%
4:3 to 16:9 Letterbox	Width 75%
16:9 to 4:3 Full-Screen	Width 133%
16:9 to 4:3 Letterbox	Height 75%

Safe Dimensions for Both Video and CG
Action & Title Safe	Action	Title	Photoshop	Pict
(720 x 486) 4:3 Video Pixel Ratio 40:27	648 x 438	576 x 389	Stuffit BinHex	Stuffit BinHex Pict
(720 x 486) Widescreen (16:9 Video) Pixel Ratio 40:27	660 x 438	600 x 389	Stuffit BinHex	Stuffit BinHex Pict
(720 x 480) DV (DVD) Video Pixel Ratio 40:27	648 x 432	576 x 384	Stuffit BinHex	Stuffit BinHex Pict
(720 x 540) 4:3 Graphic Original Pixel Ratio 4:3	648 x 486	576 x 432	Stuffit BinHex	Stuffit BinHex Pict
(864 x 486) 16:9 Graphic Original Pixel Ratio 4:3	792 x 438	720 x 389	Stuffit BinHex	Stuffit BinHex Pict
(720 x 533) DV (DVD) Graphic Original Pixel Ratio 4:3	648 x 480	576 x 426	Stuffit BinHex	Stuffit BinHex Pict