1 - Namely, I'm going to switch from my core2duo to either i3 or i5 processor. The thing is I'm not a heavy gamer (although I play games) and was wondering do I actually need to get i5, Isn't i3 enough i know it's cheaper and I don't necessary want to spend a lot of money.
2 - The other thing is motherboard, I understand I need to get discrete graphics, am I right ?? I intel's chipset, P67 but somone told me that Z68 is better. Is it really that much better ??
3 - Also do I need to get a more powerfull PSU ? Currently I have 400W.
P67 has no discreet graphics option. I would go for the z68; there's a few in the $110 range that will work fine. 400w ps may be enough for what you'll use; if you upgrade the graphics card later, it will list a minimum ps requirement. What brand is your ps?