Windows 98 is giving me disk full errors when the hard disk shouldn't be
full.

There should be 2.5GB of space. There was, until recently. The contents of
the directories add up to 6.8GB and the disc's capacity is 9.3GB (in one
big partition).

It is also displaying the file sizes of some large files as much smaller
than they should be.

I've run scandisk.
I last defragmented (although it took a lot of palavah) three weeks ago.

I have recently been working on some large files (10MB-20MB) using the
NeoPaint graphics program. These are the ones currently displayed as having
sizes of only a few tens of kB. Oddly, however, they do open OK. Apart from
one, they don't look damaged. But when I start working on them, I soon get
a disc full error.

Advice would be much appreicated.

Chris