Just enough for my drivers and my windows XP setup will be more than enough ... I will work from another partition and the system partition will be frozen ...
2Gb seem right but was using 5-10 Gb before, how much do I really need?
I'm now checking with VirtualBox If it's enough, I have access legaly to my school license ...
It used 1.11Gb on 2Gb with a windows xp professionnal cd (oem, retail, msdn, ...)
I know about Nlite but if you're not careful you will lose some stuffs that you need, but I was mostly asking for the default install size to use as a rule of thumb ...