You need to change the user-agent of the browser to download Google Chrome to Win 2K. On Firefox, go to about:config, create a new string entry general.useragent.override and set it to this Mozilla/5.0 (Windows; U; Windows NT 6.0; ru; rv:18.104.22.168) Gecko/2008070208 Firefox/3.0.1
(Note: For Windows 2000 systems the unseragent string will have Windows NT 5.0)
Right click to select new string
Enter String Name, and then enter above given value
Check your Mozilla User Agent string from Help menu of Firefox, select About Mozilla Firefox.
Note: I haven’t tested myself on Win 2K system, but it seems to work with Windows 2000 SP4.
Update: With this method you can download Chrome but not working it seems (see the comments), mean while you can try portable chrome version.