Whatever OS you go for, you should definitely consider some disk imaging software. I use XP SP3 at the mo, and have got Acronis Home 2009. I just got my computer how I wanted it to be (with Traktor etc all installed and tweaked) and saved the disk image. Now, if I get a virus, malware, whatever, and can't get it running smooth again, I just restore the computer to that image and it's sorted. Takes less than 10 mins to restore :-) Best to partition your computer into a system drive and a data drive, cos then you can just reimage your system drive without losing any files. I use Acronis, and mates use Norton Ghost, but I think Windows 7 has disk imaging built into it if you end up using that.