98%? Even if you assume this only counts desktop OSs, I think that is an exaggeration...
If I recall correctly, Apple's market share of computer sales were as low as 3% in the 1990s, and that included sales to homes and education.
I'm not sure when Linux gained traction in the server market, but I doubt it was significant prior to 2000.
I wasn't able to find web usage stats that are very old. http://www.geek.com/wp-content/uploads/2009/05/os_marketshar... is the oldest usage-based data I could find, which puts Windows up at around 97% in 2005. I can't imagine it was much lower in the late 90s, given that Macs of that era were pretty shitty and even less people used Linux back then.
And this was also a time when none-Linux Unixes were still still popular, so I would expect some share from them. Linux got a lot of momentum around '98. (Yes, and Macs existed too.) Moreover there was OS/2, BeOS, Irix and whatever... Linux however lost a lot of momentum in the early 2000s when people realized it sucks as a Desktop OS for non-geeks.
90% is well possible I think, but 98%? Never ever.