Is there a way to stop screen locking on the Captivate
Not that I know of, the longest time that you can have your screen on without timing out is 10 min I think.
There's screen locking and screen time-out. If my assumption is correct that you don't want to have to unlock the device each time you press the power button to turn it on, here 'ya go:
There are several apps that purport to do what you wish. Try each of them to find the one with features / performance that best suit your needs.
No Lock No Lock for Android | AppBrain.com
MyLock myLock utilities for Android | AppBrain.com
Go to Appbrain.com (a popular app site) and use its search function.
Separate names with a comma.