first question, have you removed the belt or has the blet broken?
if it hasn't then you want to se the engine to TDC on #1, then you want to index the crank and both cams. with this done you can remove the old timing belt. the cams will move but only by a tooth or two. when the new belt goes on then all you have to do is line the marks up and the timing will be the same as before
you didn't say if you have a pre or post 98 but how to's have been post for both in the zetec maintence forum