Was to buy a copy of Win 95 on disks, if you don't already have one. They are readily available and fairly cheap on a number of sites. Make sure you get original disks and certificate though!
Then I was able to use an external CD drive, designed for Windows, which connected via the parallel port to upgrade to WIn 98. If you don't have such a device ask around, borrowing hardware is not copyrighted!
Not simple but it worked.
Of course it may well be possible to network the portable and use a CD across the network, but I have no experience of that!
Best of luck.