If it is a text field, pressing 'enter' should give you a carriage return. Check in the Inspector -> Data -> Behaviour that 'Go to next field by...' doesn't have the 'return' ticked.
I checked the Inspector and all is as you suggested. I recently got a new computer and have discovered that this only occurs on the new computer. After opening the same Filemaker document on my old computer, it works fine. But carriage return within a text field does not work on my new computer (same Inspector settings and same operating system 7).
Any other suggestions?
Is it a laptop? The 'Enter' key and the 'Return' key do not always process the same way. I think you've proved it's not so much a Filemaker issue as a Windows one.
Keyboard settings (as in the Regional Settings, Keyboard and Mouse in the Control Panel), they're all the same? Sorry, that's the only other place I can think of looking.