I have the feeling that when I use the XP Pro cd to format and install, some of the registery entries are not erased, is this right, and if so, is there software that can be used to clean the disc of everything, including the registry entries before reinstalling?
yes if you boot from the xp cd, it will guide you through a new install, and give you the option to format the drive b4 installing the new operating system. it's resonably straight forwards. a lot of pressing enter until you see a list of your hard drives and partitions, the format option is there, it's part of the wizard so you shouldnt miss it, just keep plodding through the options
a quick format will tell the hard drive to erase the master file table i think, everything is still there but cannot be read as the links been broken. a full format will write out the drive. other options are low level formatting, the hard drive makers support site should have a download to test the drives and offer the low level format, it's only normally needed if a standard format is causing problems after a reinstall.
otherwise, what kind of issues have you come up against after reinstalling ?