First build/ need more info

[ci_vic]

I want to upgrade my PC. I only want to replace my motherbord, CPU, and my video card ( I will replace my video card a little later I just want to replace the other 2 now). I have gathererd alot of information readidn forums, mags, book about building a PC. The only thing I can't find out about is wht to do if I plan on using my exsiting HD. Do I just hook everything up and turn it on? Is there anything I have to configure before it will work right? Here is the motherboard and CPU i plan on upgrading to:
ASUS M2R32-MVP AM2 AMD 580X CrossFire.
AMD Athlon 64 X2 5200+ Windsor 2.6GHz 2 x 1MB L2 Cache Socket AM2 Processor.

I went with these because of price and user rating on newegg. I'm looking to spend $250 for the Motherboard and CPU and I am a casual gamer so I think this setup works for me (any more information about other products I should try around the same price would be welcome). Thank you for your time and information.

[Cricket]

What kind of computer do you have now? Home built or name brand?

What are the complete system specs for your current computer? List all the parts by brand and model including the power supply. Are you sure your current power supply is even compatible with current motherboards? Is it ATX 2.0 or higher with a 20+4 motherboard power connector plus the 4 pin 12v connector?

What operating system are you using now?

Cricket

[ci_vic]

I had some one at work build it for me back when I didn't know jack about computers.
CPU: AMD Athlon 1.24 GHz
DVD Drive: JLMS XJ-HD166S (not sure of the brand)
DVD Burner: Lite-on DVDRW SOHW-1633S
Video Card: NVIDIA GeForce 6200
HD: WDC WD1200AB-22DYA0 (Western Digital)
Motherboard: Not sure I was told it was one from an Emachine.
Power Supply: JPC-425 (425Watt max output).
RAM: 768MB (3 Kengston DRDD2)
Operating System: windows XP
I went under device Manager to get this information.
I'm not sure if this was the right place to go to get this information. If it wasn't please let me know where I could find it at.