Jerkiness with playback of video is often down to a mis-match of frame-rates.
There are three main frame-rates used in movies - I will round up the numbers for simplicity. They are 24 fps (progressive), 50 fps (interlaced), and 60 fps (interlaced). Some TVs can do all three frame-rates, some cannot. However even if the TV can do all three, that is no guarantee that your computer can. In particular Macs often need a lot of manual tweeking to be able to do 24 fps.
If your video is for example 24 fps, and your TV is set to 50 fps, then at best even with doubling the amount of time each frame is shown 2 x 24 = 48 and does not make an easy match to 50 fps. As a result this mis-match means either an individual frame has to be shown longer than others, or a frame has to be thrown away. Either can result in the perception of a jerkiness of the image.
If you are able to open the video file in QuickTime Player 7, you can press Command-I for Info to get an indication of its frame-rate. You could also use the free Media Inspector application see http://mediainspector.massanti.com/
If at all possible you need to set your computer and TV to a frame-rate that matches the video you are playing.
TVs are supposed to send a list of their capabilities (frame-rates and resolutions) to a device over the video cable using the EDID standard.See http://en.wikipedia.org/wiki/Extended_display_identification_data unfortunately many TVs especially Sony's are very bad at doing this.
SwitchResX for Mac can in some cases allow manually creating settings to get round this, see http://www.madrau.com/indexSRX4.html
In theory converting 24 fps progressive to 60 fps interlaced (or vice versa) should be a bit easier, this process is either called Telecine conversion or Inverse-Telecine conversion for the opposite direction. Unfortunately even many commercial DVDs have errors in the 'pattern' (order) of frames that results in it going wrong. Often this is due to stupid production houses editing video after the telecine pattern has been set, thus breaking the sequence. See http://en.wikipedia.org/wiki/Telecine