On the other hand, I agree with Tim too: I wouldn't install Win7 on anything less than 80GB for machines where I do need to install lots of disk hungry programs (or games:). To sum it up: 30 GB will be enough, if you don't plan on installing lots of disk-hungry programs like MS Office and the like. So, in my case, I would have enough space even for the XP mode (but there's no point of running XP mode in a VM. Below that, it says that XP mode requires. But I didn't install a whole lot of programs there. The official system requirements for Windows 7 state that it requires 16 GB of space, or 20 GB for the 64-bit edition.

Free memory of 256 MB RAM (512 MB recommended) 400 MB available disk space. I have a Windows 7 Home Premium virtual machine with 31 GB of disk, and it's been plenty so far (using 13 GB right now, after one month of usage.). Windows XP, Windows 2003, Windows 2012, Windows Vista, Windows 7, Windows 8. You can install XP on a different drive, so you should be fine there too. If you don't plan on installing much on that drive, you should be fine with 30 GB.

Windows 7 Home Premium 32 bit takes 9 GB of disk space installed, but you will typically need a few GB for the pagefile (depending on how much RAM you have).

How much space is needed for windows 7