I would recommend the following:
-Search for reviews online to findout how high the card might go natively.
-Make sure you have good case cooling and latest video drivers.
-Use coolbits or powerstrip to start overclocking (I used coolbits..I thinks that's what it's called). Start off small and work your way up...5 at a time.
-Once you get to a point you can't get the GPU or RAM higher you then can determine if you want to invest in extras.
-Other things to try at this point: Advanced AGP slot fan (side window fan, coolmaxx cooling, etc.), AS3 for the GPU fan, RAM Sinks (you will not see a huge increase)
-Extremes: Water cooling, Voltage, Bios Changes
Good Luck!
-JC
FYI...My Albatron ti4200p (non-turbo) is at 305/580 rock solid@stock.