is this your motherboard?:http://www.gigabyte.com.tw/Mot.../Pro...ucts_GA-7ZM.htm
You probably have a 600MHz Duron rather than a 600MHz Athlon processor; the slowest Athlon for Socket A was 650MHz
There is no such thing as an Athlon XP 1500 with 200MHz FSB. Gigabyte's CPU support lists seem to be shoddy.
Your motherboard should be able to support Athlon Thunderbirds. I don't know whether an Athlon XP would work, but it is doubtful considering what chipset you've got.
If you've got PC133 RAM, make sure the RAM is set in the bios settings to be running at 133MHz rather than 100MHz.
You could probably overclock your system for better performance.http://www.ocworkbench.com/har...gaby...e/7zm/7zmp1.htm