you mean your old Favorites to the current ones? Like, after having reinstalled the browser, or reinstalled xp?
or you mean add a page as favorite?
For Internet explorer:
if the first , then just copy the content of your old favorites folder to the one in C:\Documents and Settings\Your use name\Favorites
if the second just click the yellow star with the plus and click add to Favorites.
If U use a different browser just say which one.