No more Mac on my iMac. Just Windows bootcamp left

I'm kinda new to mac; an expert in x86 systems. I have an iMac bought 2nd hand. It has 3 partitions (1 for Windows7 bootcamp, 2. for Mac osx 10.6 and 3. a spare partition which contains an image I created using Disk Utility - in February 2011). Mac started getting slow to boot into (took about 7 to 10 mins, at some point) and one day last week I got the "spinning wheel" spinning for ever.

I reverted to using the Windows 7 until today and decided to boot into the Leopard installation DVD. Ran Disk utility and restored image. Got an error about starting. I verified disk and repaired permissions. I restarted and still got same thing. I then decided to go back into Disk Utility, erased the partition and restored from image, same result. I then decided to install mac afresh from DVD, hoping that if I'm able to get into new Mac install, I'll restore from image afterwards.

Now when I boot pressing the options button, all I see is Windows. When I boot from DVD all I get is "You need to restart your computer. Hold down the Power button for several seconds or press the Restart button.".

PLEASE HELP, SOMEONE. How do I reinstall the Mac without killing the Windows and have the option of booting from either operating system whichever I choose.