The first thing I noticed that, while the computer had 2GB of memory, some 0.5GB was being reserved by the graphics adaptor. After realising that there was no way of changing the reservation in the CMOS setup, the only option was to add more memory. More memory was added and the computer checked out. There were no indications that the hard drive was failing, and checking the task manager revealed that part of the font system within Windows was using a massive 50% of the processor. The font cache was deleted which helped, but checked for malware to find a virus that had hooked itself into the font system. The virus was removed and the Windows services permissions and default startup were restored.
Next was a cleanup, temporary files were removed and Windows and software updates were applied. The network was also reset which had the side effect of causing the network to stop functioning for about five minutes after the computer was switched on. Simply removing the network drivers and allowing Windows to install them on the next reboot resolved the issue.
The computer was taken back to the customer the very next day, connected up and internet and printing tested.