That would seem to meet our definition of a monopoly. By installing Windows 98, you'd be installing Internet Explorer. They'd be inexorably tied together. That's not to say that you couldn't install and use third party browsers, but Internet Explorer would persist beyond it's desired lifetime, and it's unlikely that third party browsers would have the same access to the operating system. Given all that, it's still not clear whether Microsoft would be violating the Sherman Antitrust Act, and if they were, what that would mean for the rest of the soft-ware industry.
Antitrust cases are notoriously difficult to prosecute.
They're complex and subtle and I've certainly glossed over a lot of issues in this short article. The real point of this article, I guess, is to promote the importance of having an informed perspective. Others look to us, the professional geeks, for answers and advice. It's our responsibility to properly evaluate situations like this and pass on educated opinions to users, rather than a litany based on propaganda. The current Microsoft rumblings are a case in point.