Can I install iphone sdk on a windows based machine(i.e windows XP), to use it with titanium. If so then guide me to do it or any link which helps me.
Just so there is no confusion, this is not so much a Titanium restriction as the fact Titanium produces a source project that must be compiled under the covers by Apple's compiler (called XCode) and Apple chooses to only make it available for OSX.
There are reports of some people having success running OSX in a virtual machine in Windows, but technically that is against Apple's terms and conditions.
My recommendation would be to get a cheap used machine, like a mac mini.
Unfortunately, you cannot develop an iPhone/iPad application on any other platform than a Mac.
Have a look at the Titanium Compatibility Matrix to give you a better idea.