What are you trying to upgrade? Do you want to upgrade the OS? If so, you could install Windows 7 on it.
If you are trying to upgrade the hardware (CPU, GPU, memory, etc) you will probably not be able to. It is time to buy a new computer. There isn't a feasible or justifiable upgrade path for that laptop.
You need to buy a new laptop, you can't upgrade the graphics, and there is no point in upgrading the CPU a couple hundred Mhz up. If you want to upgrade to Windows 7, a W7 license is $100, and it is not going to run that good.
@Wiz_27, you are talking about a laptop which is almost ten years old. You could probably upgrade the CPU (I think it is socketed on that laptop), and for sure you can upgrade the RAM, but it is not worth. Keep it with XP for light duties, and spend your money on a new system.