Well, it's been a frustrating time, but I've got it working again.
Just in case someone should have a similar problem, here's what I did.
I was having problems as I said (above) so decided to uninstall and re-install PS CS3 to try to straighten it out. I started to uninstall, and got a warning to deactivate CS3 before I uninstall it. I went back into the program to deactivate it, but couldn't find the deactivate option (it's in the help menu apparently!

) so I proceeded to uninstall without deactivating. They always say these things, but it never matters, right?

Well I don't know, but just maybe if I'd done that I wouldn't have had the trauma I was about to go through!...
After uninstalling, I did the installation... It all looked fine until the very end... then "Shared components were successfully installed" but "Photoshop CS3 and Shared Components Failed".

I tried the installation again with the same result, so I fired up the lappy and started searching the web for clues. Four times I tried to reinstall on the first might without success!

After an all points distress call (including IIS

), a work colleague dug up some information for me. I downloaded a utility from adobe called CS3Clean - I had run the beta version of CS3 before I got CS3 proper, and apparently it can cause installation problems in CS3, so they wrote a utility to clean it out.
CS3Clean had offers 2 levels of "cleaning", but in fact can do 4 levels. I followed the instructions for each of the first 3 levels, each time without success. I ran CS3Clean on a level 4 clean which I believe removes all adobe products... but part way through I got a blue screen of death!!!
The PC came back up eventually after doing a checkdisk, and recovery from a "serious error"... and all was OK apart from the loss of all adobe software. Too much fun for that night so I packed up.
I took a break of about 2 days before I had another go at it. This time I tried a few other things that people on the web had advised, without success. Eventually I went back to the instructions for CS3Clean and followed them
to the letter! But as well as that, prior to running CS3Clean I disabled all my antivirus/spyware software.
I really didn't expect the installation to work, but it did!


Not only that, but I had been having problems with some components of my antivirus software not working (and the software company has given up trying to help!) - and now they work too!

Hmmm... coincidence???
Al.