Bare-minimum hard drive space to install Windows XP SP3 Professional?

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 ...

This is just a possible solution to make the XP Install take up less space.

Have you ever heard of nLite? Basically, it allows you to add/remove components to a Windows XP installation (e.g. drivers, applications, services), and create an unattended install if desired.

I always remove the stuff I don't need from Windows (e.g. firewall, defender, wireless services, indexing) to save space and increase performance (also, there's no point on keeping the Microsoft versions of software if you replace them with something else anyways).

I created one version for a Virtual PC, so I basically ripped everything out of it, and got the final install size to under 300mb (and if I compressed the image with WinRAR, the virtual hard disc shrank to ~165mb - the same size as the ISO). On my normal XP disc, which retains most functionality (including wireless), the install was about 400 to 500mb (without a pagefile!).

A lot of stuff is done on the partition that Windows is on (think temporary files from all types of files). I once ran out of space while trying to extract a large set of files from an archive, even though I wasn't extracting to the partition Windows was on (but the unarchiver was saving some temporary files there). Also, a few programs, although installed on a different partition, copy some files to C:\Program Files\Common Files (that folder is taking up nearly 650 MB on my PC).

On top of the minimum 4 GB everybody is recommending, I suggest you leave a little bit more, just in case (about 1GB should be enough); it never hurts to have a bit of breathing room :)