How to install Snow Leopard from XP on MacBook?
you have to make a bootable usb disk.

Transmacfor for Windows (2-week trial) can format USB drives for mac and restore .dmg files to USB drives.

http://www.asy.com/scrtm.htm

Download Transmac and install in Windows
In the right-side panel of Transmac, right click on your USB Drive >> Format Disk >> Format with Disk Image
Point to your .dmg file and click Open.

your USB Drive has to be at least 8GB.