Basically, what I'm looking for is a piece of software that can count the BPM of an inputted signal via something like a line-in, so that I could more easily ascertain the BPM of my friend's performance (he's a vinyl DJ) so that I could jam along with him without having to pause and count BPM's (my beat counting skills are sub-par at best, you see). Ideally, the program could also output a MIDI tempo signal that I could make something like Reason/Ableton sync to, but this isn't a *must* however, just the live beat-counting would be great. Anyone know of a solution to this?

PS: Yes, I am aware that obviously real-time midi syncing from a line in would be fairly CPU intensive and glitchy (from what I've read from random articles/etc at least) it's more a dream/wish than an actual belief that there's something out there that does this.