Can't help you unless you let us know what type of computer and TV you have.
If it's an old TV with a coxial aerial input or a SCART, then it's more difficult and the results won't be great anyway.
If you have a modern flatscreen TV, then it's likely you'll have VGA, DVI and HDMI so you'll manage something - possibly through all 3!
Anyway some TVs work better than others as monitors as you might not necessarily get a neat 1:1 pixel mapping. Modern 1080P sets are better in this respect. For older 1376*768 sets, Samsung and LG work best.
I have a cheapo LG which allows you to switch between a TV or computer input on the same DVI connector - it changes the overscan (why oh why do we still have that with digital TV!!) and colour balance.
I recently fitted a cheap graphics card with an HDMI connector, I now get pictuure and sound perfectly - this is the best way to go if you can.
Oh and don't be ripped off if you buy an HDMI cable. Mine cost £4 and works perfectly.