Ok.
If I plan on making my comic in MS Paint (Shut up, I can use illustrator)
what size should I use?

Actually...I DID one in illustrator and DD was too small for it or my AI file was too large. Like, width wise.

So, what size? Width more specificly.

I usually stat with a canvas that is twice the size of the final Piece I want (For 8 1/2 x 11 I start with 17 x 22). I also use 300 dpi to start. When I'm done with inks and colors, I re-size to 1/2 the original size and set the resolution down to 72 dpi.

That's just ME, though.

In Illustrator, when you "save for web", you have the option to edit the pixel dimensions. If your page is vertical, 600-500 pixels wide can be the sweet spot.

Actually, I personally use 800 wide if I'm doing anything full-page size. Height can be any length you feel like, but I personally try to keep it on or around 1000 pixels.

Well, I did a few comics in paint. And I think I got the dimensions right:
http://www.drunkduck.com/Alt_0252/?p=33506