Hi Samuel,
Major difference between 98/Me and NT/XP/Win7 version is Unicode support. This mean 98/Me could not correctly handle multi language documents or Unicode code pages. From another side, non-unicode version uses twice less memory, because all texts are stored as single byte.
In addition to this, 98/Me version does not use some new functionality available from Windows 2000 and later as Alpha icons, Layered windows etc.
But generally you can run 98/Me version on any machine. In addition, I can say that non-unicode version is much less tested. Regular checks that I do, that it is runs on 98 and can open/edit files.
Best regards,
Alex.