Just right-click on the title you don't want in the list of songs it is selecting from (to the right on the 'Now Playing' tab) and select Remove.
Member of UG's Tubgirl Virgins Club

You can't, unless you delete them from the playlist. Just make 2 playlists, one for random and one for normal
Remove it from the Now Playing list. It'll take it off and not play it, but it'll still be on the playlist next time you load it up.

If you decide later you want it back on, load the playlist again or just put it back ont eh Now Playing list.

Or, just skip the song when it comes on.