User Tracking don't seen users MAC's and ports on 1924 switches (other switches OK), but all 1924 switches have been discovered and exists in Topology View. Software version on 1924 - 5.37, and upgrade is not possible, because 1924 very old. How I can tell User Tracking to discover MAC's on 1924 too?
1900 series switches require 8.0 (Enterprise) version as minimum for Campus/UT to support them. You can look at http://www.cisco.com/warp/public/477/Campus/ani.shtml to see if it helps.