have u got service pack 3 install for yr win2k ?, is yr mother board using a via chip ? if yes install via4in1 4.40, get it from
http://www.viaarena.com , make sure yr display card driver is new, win2k & winxp always have a refresh rate problem with display driver maybe u should check that ? im not sure with ati driver coz i never bought a ati card b4, ill all use to 3dfx & nvidia only ^^ , sorry if i cant help, oh ya try disable the mouse smoothing in CS ?