There are some known problems with the IE6 Public Preview and Win2K. Here's what I know (I think):
If you are running Win2K with SP2 and then install the IE6 Public Preview, the Add/Remove Programs applet loses track of the SP2 entry (so that it can't be uninstalled).
Some people who have had this happen have mistakenly thought that this meant that they had lost SP2 on the system, a natural assumption for anyone who was used to NT4, where you had to re-install the last service pack after practically every change in the system configuration. So, they would re-install SP2. When they did so, IE6 would disappear from the Add/Remove Programs applet! Cool, huh? (Note: I've seen some discussion of this indicating that the IE6 disappearing act only occurs when the SP2 re-installation is performed with the backup feature disabled. But I've seen some assertions that this doesn't matter.)
Anyway, that's all I know firsthand about it. It's obvious that the Add/Remove Programs applet can be affected by this combination of OS and service pack and Internet Explorer versions, but I'm not sure about the applet being disabled altogether. Of course, I also don't know whether your IE6 version was the final version or the preview version, and I don't know if that would make any difference. My suggestion, all things considered, is that you should NOT upgrade to IE6 in any form -- that's if you stick with Win2K. IE5.5 SP2 is a decent and secure browser. IE6 is better, IMHO, but not worth screwing up the OS for!
Someone else around here may well know better than me about this. If so, I hope they'll speak up. We should look around for info on the combination of Win2K, SP2 and IE6 to see if anything turns up in places like the MSKB. I'll get back to you here in this thread if I find anything. Sorry I don't know anything more specific.
Regards,
Jim