This story on EvEm.org.au gives the lowdown on how to restore the long-lost crosshair health function in Quake III Arena without any files or modifications, simply by using some Q3A console commands. The downside to the technique is that it involves setting r_picmip to "0" which needs a pretty beefy system to handle without too much of a performance hit. However, if you can run the game acceptably using these commands, it will allow you a razor thin circular crosshair that indeed gets redder as you lose health.