Problem is that a modern stylus will bottom out on a 78 groove, or certainly ride very low. You really need a specific stylus for the groove format of 78's.
I get around that problem by having an old Shure M75EDII with an N75-3 stylus for my limited 78 collection.
And that is before you get into the different EQ that is used on 78's from different manufacturers and ages. But I think Audacity can cope with that.
Aha - yes it does
http://wiki.audacityteam.org/wiki/78rpm_playback_curves
Craig