I have a samsung omnia w 8350 with windows 7.5, I want to install Android OS on the phone, can anyone help?
Doubtful. A Google search suggests that even getting custom Windows 7.5 firmware installed is difficult, let alone a wholly different OS. In theory it should be possible, but I think you'd be better off getting an Android phone instead of waiting.
So far, we haven't even gotten custom WP7 ROMs to run on the Omnia W. In fact, we don't even have a flashing tool to replace the stock ROMs with.
I only know of one Windows phone that got Android on it (HTC Photon) and it was because the hardware was basically identical to an Android-based phone (HTC Legend) that was put out by the same company, it was a simple port.
The reality is that the phones hardware likely doesn't have proper Android support. This could require writing drivers from scratch and creating many interface layers (like interacting with the camera). Many times this is extremely difficult even if the phone does run Android due to the code being closed source. In fact, many times manufacturers will change the drivers to interact with the OS differently than Vanilla Android, so just trying to get a custom ROM working on the device can be a nightmare. This is why many devices aren't supported with 3rd-party ROMs like CyanogenMod or AOKP. The developers just can't reverse engineer things to work properly.
So, it wouldn't be as simple as installing Android, because you would have to fully port Android over to the device and be a highly skilled programmer to do so. It would most likely require a lot of reverse engineering and debugging just so their custom drivers would work. Simply put, it just isn't worth any developers time to try and attempt this. Their time would be far better spent starting with a device that already has Android running.
And even if they were to get some basic support, you would likely have many functions of the "smartphone" not working, such as GPS or wifi. Your money (and sanity) would be much better spent with getting a device that runs the OS you want.