Car Trouble Re:Possibly with Motor

Recently my 1987 Cadillac Deville broke down. When ever you press on the gas you can hear the engine trying to work but unfortunately it doesn't move. Luckily it broke down at a friends house about a mile from my house so I was able to transport it back to my house, but it took quite some time. Once I got it moving it wasn't moving like it should, but the more it moved the better it worked. When I returned to my house I popped the hood and I saw that there was anti-freeze leaking from the motor. Do you think the transmission is going or is it something less fatal?

P.S - It is the winter time here so it might be that something is frozen, but everytime I use it, it runs for a good 10 minutes before I try driving it.