Hello and welcome to the forums
Well first of all we don't have anything called a 64-bit motherboard,i think you mean the motherboards that support 64bit CPUs,if so then your motherboard support them as well,also socket 775 is out of production so either keep your current motherboard or upgrade the CPU too.
P5W-DH is a good board,do you have any problems with it that you want to upgrade it ?
If you worry about DDR3,then don't because the difference between DDR2 and DDR3 isn't noticeable in games/most apps
To clarify yes, I mean I want a motherboard that supports 64-bit architecture (I plan to get 64-bit Windows 7). I have a Q6600 G0 which I believe is compatible so I just need a motherboard. I also thought that I might aswell upgrade to DDR3 as I can get 3GB triple channel for around £100, which isn't bad and I'm fine with that.
I've done some digging and came across the Asus Striker II NSE. Is this OK? Also I noticed the Asus Striker II Extreme is around the same price - which is better?
Your motherboard supports Windows 7 but if you want to upgrade,then between those boards i couldn't find any differences between them in terms of cooling and PCI-E slots,so go for the one which is cheaper
From what I've been able to find it appears to me that the board you have will accommodate the Q6600 so since you have the board and I'm assuming must have memory for it then why not try it before spending more money for next to no noticeable performance gain.
There isn't going to be that much difference between DDR2 and DDR3.
Probably all you'll need is a BIOS flash and you might well be good to go.
I find Win7 surprisingly good at finding the drivers it needs all on it's own and I'm using 64bit version.
The worst thing I can see happening is maybe an issue with drivers for the board but it won't cost you anything but a bit of time to try it and find out.