I finally got around to doing it... I've reinstalled Win98 and it has cured my dll problems.
Another forum (that I went to when PCA was down) said not to do it. They said that nothing would work and I'd have to reinstall lots of software but so far the only thing that doesn't work is BootMagic. Thankfully PartitionMagic works just fine so I now have a backup copy of my fully functional C: drive.
My thanks to everyone who has helped me with my dll problems. I just wish that I had bit the bullet and reinstalled when it was first suggested a month ago.
For some reason I had a mental block against doing it. I really don't know why as I've quite happily flash upgraded BIOS before now (installed an 80gig HDD). It was as though I thought that something would go wrong but even if it had all my data was backed up so I could have just started again from scratch.
Many, many thanks,
PS ...and flushed with success I finally got around to upgrading to 98SE too.