K2 works well in W2k here. I run it in stand alone mode on a second computer (P4, 2.8 gHz, Intel 865 GBF, 2 gigs ram, 3 Seagate hard drives) and it works with EWQLSO, Symphonic Choirs, and StormDrum. It's great being able have four ports and a lot of MIDI channels.
A minor nag I have come across is that K2 takes about ten to twelve seconds to initiate whereas Kontakt 1.53 initiates in about two seconds or less. Perhaps this is idiosyncratic to my set up. Other than this, it seems quite stable with W2k.
Thanks for the replies. It is good to know that I won't need to upgrade from Win2K. I can get Kontakt for an upgrade price from GPO and EWQLSO Silver so it seems that would be my best bet for a sampler.