Put current Hard drive into new pc.

I have just bought a new motherboard processor and RAM and want to use my existing hard drive in my new setup. What do I have to do to the hard drive to put it in the new computer? Can i just put it in my new computer and WinXP will find the new hardware or do I have to do something else first? My components are: ECS K7S5A with AMD XP 2100+, 256 PC2100 DDR RAM, 40gb Western Digital HDD, running Windows XP. I am really stumpped and would appreciate the help.

Thanks Robert