Thanks to everyone for your support and info as i've made my formal decision. It was somewhat hard to find the particular motherboard (Asus M4A785-M) here in Australia, as it's apparently at the end of its run of make (thats what i was told!)
Now heres the funny part, the motherboard in the Compaq didn't die, the battery on it did, so I replaced it and wouldn't you know, it works!
But the stupid thing is, I broke some pins on the original CPU (AMD Athlon 64 X2 3800+), now i'd also like to know IF an AMD Athlon 64 X2 5200+ would be compatible with this particular motherboard (Asus A8M2N-LA or as its also known as HP/Compaq motherboard name: NodusM3-GL8E) ?
This is the OPN tray no: ADO5200IAA5DO for that particular AMD Athlon 64X2 5200+ processor, found on ebay Australia.
I know from the hp support website that the mobo can handle up to the 5000+ but another website i've seen reckons one can run up to a 6400+ version of this CPU with an update to the BIOS on that mobo.
All your feedback has been helpful and appreciated and more support and info for this other dilemma will be greatly appreciated, too. Thank you.