I was interested in your problem, as I make a lot of use of DOS and BASIC.

You didn't say which type of BASIC your friend uses ie. GWBASIC, QBASIC
or any of the other dialects of the language. IIRC the very early PCs
had BASIC installed in a ROM chip, then there was BASICA which was on
disk. How did it get transferred to Win98? Is the program being run in
interpreted or compiled mode?

Why make any changes if the existing system is working OK?

There isn't much support for BASIC running under Linux, although there
are one or two versions available. Most Linux programs are written in C.

I can strongly recommend BBC BASIC for Windows, available from
www.rtrussell.co.uk Its a very powerful, yet easy to use language,
with excellent support from the author. I use it for all new programs,
and it is one of the reasons why I still use Windows...

BTW I still use native DOS on an older PC, for a couple of office type
applications. This dual boots with an older version of Ubuntu.