Thanks for the update Rich. Please update the discussion if you encounter further difficulties. The discussion may need to be moved to the Installing, Updating, & Subscribing forum at Installing, Updating, & Subscribing to Acrobat if Acrobat continues to fail to obtain it's license from the CS3 installation.
You did remove all Adobe software prior to reinstalling CS3 Rich? If not then please do so and then complete the steps listed in Resolve "temporary activation expired" error for CS3 and Acrobat 8 prior to reinstalling Creative Suite 3 and Acrobat 8.
So, Resolve "temporary activation expired" error for CS3 and Acrobat 8 wasn't much help because I'd already done everything it suggested when installing the new CS3.
So I have found another way:
1 - Using the uninstaller (found in Applications/Adobe Acrobat 8 Professional/Acrobat Uninstaller), I uninstalled Acrobat.
2 - Then, using the new Creative Suite Setup installer, I unchecked everything except Acrobat and installed that.
3 - Once that was done successfully, I launched InDesign, then Photoshop (neither of which needed a serial number).
4 - Then I launched Acrobat and it initialised without a serial number and is working just fine.
This can be forever known as The Rich Solution.
Thank you for your help. I'll post again if it all falls over again in the morning!
Rich