If I recall correctly, Excel 4 had good support for reading and writing via DDE. If you're going way back, you might as well go waaaay back. I haven't used any myself, but Google shows several listings for Java DDE support. If nothing better pops up, you might give it a try.
Have a look at JODconverter, which uses OpenOffice, where the list of support documents includes MS Excel 4.
If you can't use it directly, maybe you can convert to an intermediate format that works for you.
If I recall correctly, Excel 4 had good support for reading and writing via DDE. If you're going way back, you might as well go waaaay back. I haven't used any myself, but Google shows several listings for Java DDE support. If nothing better pops up, you might give it a try.