I want install Windows 7 on my Macbook after I formated Snow Leopard
You need to boot from the OS X install DVD which was bundled with your Mac (start the Mac with pressed C while the DVD is inserted). Launch "Disk Utility via "Utility" in the menu bar and create a partition which is "MS DOS FAT" formatted. If its done replace the DVD with the Windows install DVD and boot again with pressed C button. After the Windows install assistant has started, reformat the partition to NTFS and continue installing Windows.

Be aware that Windows OEM versions won't work. It must be a retail version.