the free apps in the app store are not trials. they will continue to work, they are just limited in functionality compared to the full version of the apps.
As somebody else said, make sure you are on the 2.1 firmware, as that fixes a lot of the problems with Apps. If you have the 2.1 firmware already, there are a few things you can try.
1.) Reset your iPod. This won't cause you to lose any music, high scores for apps, videos, etc. Everything will stay on there. It will just help things to run smoother. To reset, hold down the home and sleep buttons till the screen turns off (when the option to turn off comes up, just keep holding the buttons down). Once it has shut off, hold the sleep button down to start it back up. It may take a long time to start back up, thats normal (1-3 minutes).
2.) Reinstall the apps that are causing you trouble through iTunes.
your trick worked ..props to you ...what did that actually do to make it work..if you dont mind me asking..thanx man