In theory an Intel mobo should be the best one for an Intel processor
That looks fine but wont upgrade to DDR3 at a later stage but with fast enough DDR2 ram that shouldnt be a problem.
A bit of a dilemma here for you Simon.
The Q6600 is only a 1066MHz one and this mobo and the Asus you mentioned are capable of 1333Mhz.
Theres a core 2 duo which is 2.66ghz and 1333Mhz which is slightly cheaper, comparing both on Ebuyer, possibly cheaper still elsewhere :
http://www.ebuyer.com/product/130484That should be faster for single applications than the quad.
There arent any applications out yet that I know of that can fully utilise dual core CPUs, only a single core at a time, although they will come along I am sure.
The advantage of a multi core CPU is that you can run 2 or more heavy CPU intensive applications at once without one application taking some performance away from the other.
Are you likely, now or at some stage in the future, to be running more than 2 heavy duty apps at the same time ?
If the answer is no then the core 2 duo is probaly your better option, bang for buck.
If the answer is yes or you think that some programs and/or games will be coming out soon that can make use of all 4 cores then you are better off going for the quad.
The ram you mentioned would be fine with that mobo and is the fastest it will support.
You will need a PCI e GFX card and as Jester has said depending what you use it for then any of the ones hes suggested will be ok.
I prefer Nvidia to ATI but thats just my personal prefernce and I am not a gamer.
I am using an 8400GS in this pc but that was just so I could get the Aero desktop feature working on Vista which my old agp card wouldnt do, this mobo has AGP and PCI e slots so I can use either.
IDE and Sata drives mix without any problems, unless your an old scottish woman
You may find that you will have to get a PCI IDE controller card if you wish to use your old IDE drive and a pair of DVD drives, unless you get a new SATA DVD drive for one of them.
The PSU should be ok just check that it has the 24 pin mobo connector and at least a 4 pin intel cpu mobo connector, some use 8 but that mobo just uses 4.
Also that it has a GFX card connector.
I hope I have covered everything, if you think I have missed something or want to discuss something else just ask