Replaced my old 3GB hard disk with a Seagate 20GB. When I finished the install it's capacity was stated to be only 3GB, as before, (I thought I enabled large disk support & FAT32. What did I do wrong or is it a BIOS problem (Phoenix BIOS, PII 200 & W98)?

Sounds like it isn't an autodetecting BIOS, you might have to clear the existing settings out and get it to redetect the drive.

If you still have problems, look on the Seagate site, there's disk setting up utilities on there.