More than enough. We're at that that point in time in terms of emulator progress where we are trying to emulate 6th-gen consoles and beyond. High demand games from recent years aren't emulated well by any standards, so performance isn't really the issue.
I run Pentium 3's between 600-1000Mhz with no problems up to the polygon era (with a few exceptions like Midway games MK etc.) so your spec is more than enough to run most classic games, a fairly graphical front-end and some additional software. To get the most in terms of speed, as always, think about using a faster OS like XP Lite or Tiny XP, Linux etc. and remove any unnecessary running apps.