mobility radeon 7500

I use a Dell C610 laptop at work with an M6 ATI (16MB) ATI chip, and it works pretty much the same as my 8887 M9. Here's basically what you should do (apologies if it's over-simplified):
1. Plug in your CRT to the back of the laptop (and turn on the CRT).
2. Open the laptop and boot up.
3. Both screens "should" come on and show the same thing. Not to worry if they don't.
4. Right-click on your desktop background and click Properties.
5. Click the Settings tab.
6. Click the big, square "1" symbol. Check boxes below should be checked but grayed out, and say "Use this device as my primary monitor" and "Extend my Windows desktop onto this monitor".
7. Click the big, square "2" symbol. CHECK the box below that says "Extend my Windows desktop onto this monitor". Also adjust the screen resolution as necessary.
8. Click the APPLY button at the bottom.
9. Both screens "should" come on and your cursor should move ALL THE WAY RIGHT and back if you are getting extended monitor. If your laptop is sitting to the right of your CRT this will seem backwards at first.

If you get this working, you can now go into Advanced settings, Display tab, and fiddle with which monitor is on or which monitor is primary.

It would be helpful to know what you're working with. What hardware, laptop, what OS. Perhaps an older OS like Win95 doesn't support it. Dunno. Give us more info and let us know how it goes.