|"Kindly tell me how much max. RAM size is supported and harddisk size"|
Hard drive size shouldn't be a problem, memory is limited by both the board & the OS. If you're going to stick with XP, there's no point installing more than 3GB. I see you're still running SP2, why? SP3 was released almost 5 yrs ago, what are you waiting for?
"Motherboard:Intel(R) 82801GB/GR(ICH7 Family)
Intel(R) G33/G31/P35 Express Chipset Processor"
Where did you get that info from? It's generic & related to the chipset the board is based on, it's NOT the make/model of the board.