Probably just condensation. That's totally normal. If you're getting any coolant in the exhaust, you can probably smell it.
Put your hand over the exhaust pipe and see if it smells like anti-freeze or if the liquid has that slick feel like anti-freeze. Chances are it's clear water - just collected condensation in the exhaust. That should clear up after the car fully warms up and you drive it some.
Edit to add: if the water is coming from the muffler, not the tailpipe, that sounds like you have a hole in the muffler. Where exactly is the leak? Muffler body? Pipe to the muffler? The Fiero exhaust is stainless steel, so it shouldn't rust out, even if it sat with water in the muffler all winter. (not uncommon if the car was stored all winter outside in a cold climate)
[This message has been edited by Formula88 (edited 04-10-2007).]