I thought it might be W98 SE .
This won't help with you BIOS problem but if you want USB to work a lot better in W98 you need to see if you can still get this file : " NUSB31E.EXE " .
I have a copy if you can't download it from some web site .
I'm not sure how to get it to you though.
I have an old IBM desktop still in operation 300PL about the same vintage as the Thinkpad 600e . The BIOS in it is from 2001 & the last one that was created.
It still doesn't boot with USB even with that BIOS update.
What you are probably going to need to do is get a USB floppy drive.
Get the BIOS diskette & create a bootable CD with it .
I'm not sure how to do that because I've never needed to .
My IBM desktop still has a working internal floppy drive.
If someone posts some instructions I will give a go at creating one with the BIOS I have to see if it works . I won't reflash my BIOS since it is working but I would test it up to that point.