By not working, do you mean they don't function properly or that you don't want to use/see them? As mentioned, alternate launchers can hide the apps without rooting and removing them.
- If it's just an app or two, go to the market and update them if possible. This may replace any corrupted data. You can also go into applications (menu>settings>manage applications) select the problem app and clear its data and cache.
- If you have several stock installed apps that don't function/ force close, you probably should consider hard resetting the phone. This will refresh all the stock apps, but you'll have to configure the phone and re install all the apps you previously installed.
Good luck!