I knew it is becasue of pixels ,right ? the more pixel u have , the better it looks on computer screen, then should i always go for greater pixels if I do editing on computers and want to know what it exactly looks like before i put it on TV ?

Possible explanations:
A lot of TVs have the contrast and saturation set greater.

On a TV set, all the "pixels" blend together and you don't see each individual dot. If you're looking at a computer monitor, you can see each dot/pixel.

2- If you do editing, check everything on your TV. You can get a blue gel and quasi-calibrate your TV so it's closer to being accurate color-wise.

oh ,one more question,does pixels matter if I only play it on TV ? I mean will more pixels make the picture 'look' better ?

When uploading and editing, hook up your capture camera like if you were gonna capture, but also use the a/v cables from you capture camera to a tv.
By default, the footy should show on both the tv and the computer monitor.
If not, you should be able to do it somehow.

there is a bit more to it than just the pixels.

ntsc and pal are television standards, not computer monitor standards... there are things like interlacing on the video footage that may not be getting handled correctly on your computer monitor... and your computer itself may not be fast enuf to play back all the video frames as well.

there is also the issue of correctly adjusting ntsc gamma settings and color balance on a computer monitor... it can be a real p.i.a. if you don't know what you are doing.

follow glenn's advice, you'll be a lot happier in the long run.

Check the field order when you're importing video into these programs. I think lower-field first is the most common. Mess around with that a little and see if it looks better to you.

oh ,one more question,does pixels matter if I only play it on TV ? I mean will more pixels make the picture 'look' better ?
Are you talking about your camera or your computer/TV monitor?

Your computer/TV monitor will not affect the resolution of the final product. If you want to know how your final product will look like, hook up a normal TV to your computer (use a camera/deck as a DV-->analog convertor). Keep in mind that colors will not be accurate unless you are using a calibrated professional NTSC monitor. Most people won't need to spend money on one of those unless doing color correction.