WIN2K is installs in a different directory from win 98 - usually in a folder called WinNT so I'd doubt the problem is with the OS.
Are you using IE 6.0? (I.E 5.0 is buggy and not supported by some https sites)
If you are, have you tried changing all the settings of IE back to default values? (and then closing and re-starting the browser to see if anything changes).
And have you tried it with a different browser, like Opera?
hth
Charles