1. Prepare The Boot Disk
Download iBoot & Burn a Boot CD
2. Insert the iBoot and boot
3. Eject the disk when you will see the following screen
4. Insert the Retail Mac OS X Snow Leopard DVD, wait a few seconds
5. Press F5.
6. Select your language and click the arrow to proceed.
7. partition your drive. Click on Utilities > Disk Utility.
8. Select Disk and click Click Partition.
9. Select 2 Partition for the partition scheme. as you will install windows 7 on other partition.
10. Select Mac OS Extended (Journaled) as the Format.
11. Click Options select GUID Partition Table, and then click OK. — You have to do this otherwise you will not be able to install Mac on this HDD.
13. Ok, and carry on normally to complete the installation.
14. After complete, you will get a boot error.
15. Eject the Mac OS X Snow Leopard install DVD, put your boot CD back into the drive, and reboot the machine. Now when you boot up, you should see a second choice for your installation partition
16. Sorry for me it failed after this stage so I had to put my windows back. I am adding all the references as below if anyone would like to give a try