My car just started to make a loud noise when I turn the engine over; I'm fairly certain it's the harmonic balancer. Will I do a lot of harm if I need to drive just a little with it making that noise?

If the harmonic balancer is loose from the crankshaft, and that's the only way it can make a noise, then it could come completely off and do a lot of damage.

Jericho is right. If it comes off, it will most likely tear up anything it hits, causing lots of $$$$ damage. But the news is even worse. A bad harmonic balancer can start to wobble and cause cause so much stress that it can crack off the front of your crankshaft. Then you're taking a new engine. Get it fixed while it's a small problem.

I would only drive it to a repair shop, provided it's not far away.