How to install OS X on same drive with already installed Dell d820 with W7Ultimate?

[sorro]

So i have a laptop not very new model.
It is Dell d820, C2D T7200 CPU, 2GB RAM, Nvidia,
motherboard model: 0JF242
chipset: Dell 955XM/945GM/PM/GMS/940GML Express Processor to DRAM Controller

It has one big enough SATA HDD inside with Windows 7 Ultimate (build 7600) installed on it. Disk is formated to NTFS as it is default to Windows 7 during install.

My question is:
How can i install Mac OS X 10.6.3 retail (I have iso image and DVD ready) on that same drive without Deleting Windows 7 ?

I already tried to follow couple of tutorials that suggest to shrink the disk and then install OS X on it. However when i try to install OS X installer asks for GUID disk which i can not create without deleting Windows 7.
Any ideas on that?
Is there any other ways or tutorials...