No it will not overload the CPU. 2 GB works nicely with Windows XP you will not get much "bang-for-the-buck" with a memory upgrade.
You need to check if you have open motherboard memory slots and that the motherboard supports more than 2 GBs of memory.
If all your memory slots are currently used then you will need to remove some of your current memory modules and add larger ones. Or you may have one of those boards with 2 SDRAM slots and 2 DDR slots (normally 2 GB max) - you can only use one type of memory and can't fill all the slots in that type of board.