Just to update those who may be interested, I couldn't piggy back the hard drive into my old PC, because it was SATA and my old one is all IDE, so that idea was killed on the spot.
What I did then, was to start looking at the Services and Applications that I mentioned had all been disabled, and found that by selecting Properties, then choosing Automatic from the drop down menu, some of the services could be manually started. I managed to suss out which ones were related to Plug & Play, external drives, etc, and also managed to get some programs running, so tried again to install SuperAntiSpyware, this time successfully, but each time it ran, it kept freezing, so gave that up as a bad job.
I managed to retrieve the treasured photos to my external drive, so once I knew they were safe, I felt more relaxed about delving into things, so inserted the Dell CD and rebooted. After getting it to boot from the CD, I tried the Recovery console, but couldn't make head or tail of it, so went for the Repair installation option, which seemed to go OK, but produced some errors about missing .dlls, which I think were connected to the spyware. I ignored the messages, but when it came to start Windows, it got to the first Windows screen, then it all just went blank, and wouldn't go any further. I then decided the only course of action was to do a clean reinstall, so that's as far as I've got tonight. I did create a separate partition for the Windows installation, leaving the rest for documents, so that should hopefully act as a safety barrier, should anything like this happen again. I shall now be spending most of the morning setting Windows up, and installing programs, but at least it's a nice fast machine to work on.