There are many threads, articles, tutorials etc. on this subject, so you should check them out, before asking here. For example, you may visit my thread named "Yet another framerate independent movement in SDL", it's in this forum. There you'll find one good, working code example of independent frame movement.

Additionaly, you may check this out: http://2dnow.zenzer.net/viewarticle.php?a=5. There's also one article here on GameDev.
And remember: google is your friend :-]