I have used ABC2Win to translate from ABC to sheet music, it's $20 to register (which I haven't done yet--sigh). The unregistered demo version will translate to sheet music on screen but won't let you print it. I have found it to be quite easy - the best way of entering music note by note I have found so far. Easier even than scanning it in and going back to correct errors using Musitek's MIDISCAN (see above in this thread). And if you've already got ABC files it's as easy as falling off a log, but a lot less painful.

But if you're a Mac user, look at my post of a few minutes ago on the "Internet Music 101" thread for a link to a site that has some Mac ABC programs.