Ok Dave,if it said it formatted in about 10 seconds then I dont think its fully formatted.Go here to get the full info on Fdisk.
http://support.microsoft.com/default.aspx?scid=KB;en-us;q255867#5
It looks daunting but its easy peasy honest
You need to boot up with your win 98 boot disk in and at the A prompt type Fdisk then hit enter
remeber you are now in Dos and the mouse wont work so its keyboard stuff from now on .
Make sure you are on the correct drive,which should be easy to identify by the capacity of each one as you dont want to wipe yor primaary drive.
Read the instructions on that site then all you do is delete any partitions on your drive,create a new on at max permitted size in FAT 32,do not take the option to make it bootable unless you intend to use a different OS on that drive.Even if you just want it as one drive it still needs a partition but the partition it creates will be the full 120 gigs.
After it has done its stuff I usually close down and then reboot again and type Format D at the A prompt,( I am not 100% certain if you need to reboot between fdisk and format but I do ).
Sitback and wait for ages then it should all be ok.I think a 120 gig drive will take a fair time so may be better doing it when you go to bed
Hope this makes sense and sorts it out for you