how does the software work that only lets you use trial versions once? how do you get around this for free, edit the registry?
Never heard of a trial that only works once. Generally it would be 30 days, 30 times, unlimited time and tries, but with restrictions, etc. Sure if it used the registry and you knew which key, you could delete it (the key) after each run. You could try a registry monitor to see what keys it accesses. Pay for it if you really want to use it or see if there is a freeware alternative.
Before you downloaded it, how long did it say that it would give before not working. what software was it?