i just put in a AMD Athlon XP 2500+ CPU Barton 512K 333FSB Socket A 462 into my system but on the startup page it says its running on 1100+ and had something saying i cud change the cpu speed by going into bios settings but i have no idea how to do it.
it sounds like you have an Althon XP-M, not just a plain Athlon XP.
the XP-M was a mobile version (for laptops), it's multipliers were unlocked. often times when installed in a desktop computer/motherboard it will default to the lowest multiplier (in your case, resulting in the CPU being recognized as an 1100+
if your motherboard allows CPU multiplier adjustment then it's an easy fix, but not all motherboards support overclocking. what model motherboard do you have?