Have you contacted Lab volt about the options ?
Like other equipment, it may be that the latest firmware is not compatible and you 'brick' the lathe making it unusable.

It looks like the easiest is 2. download the lower version (Level 4) software into the PC
But can you do this ?

Looking at option 1.
There is this USB 2.0 TO RS232 Serial DB9 9 PIN Adapter Cable GPS PDA UK | eBay
and it says it compatible with Windows 98. I don't know if it will work in your case but it won't cost much to try.