I can no longer get the "Puzzle Goal" window to display. I've tried enabling/disabling it though the "Windows" menu with no luck. The "All Parts" and "Playfield" windows display correctly, as does the toolbar. Any suggestions?
This is on Windows XP. The last time I played the game the window would appear, but once I started it up today it's no longer there.

I got the same problem !!!
I try to reinstall but it's still disappear!

What I've done is keep a browser open on this url:
http://www.gamefaqs.com/computer/doswin/file/30270/21076
It has the goal listed for each puzzle, you just need to be careful not to scroll too far or you'll see the solution.

I've got the same problem, but it's with the part bin. It happened when I was adjusting it to try and fit the whole of it on my screen, so I think perhaps it's been moved offscreen somewhere.
(Edit) I've confirmed that my problem was indeed the window being moved off the screen. Deleting timwin.ini from C:\ (Not the copy in the TIM3 folder) fixed it. Hopefully the same thing will fix peoples problems with the Puzzle Goal box not displaying.