OEM Wheels?

[Energizzzer]

I purchased a 2006 750Li about six months ago. The vehicle is equipped with what appear to be 18" chromed 545i Sport Style wheels? The guys at the BMW Parts Store ran a VIN check for me and these were not installed at the factory - no surprise there!
I am in need of tires and considering replacing the wheels for a different look. How do I determine if they are OEM equipment or simply aftermarkets with BMW center caps?

Thanks in advance for your response.

http://i967.photobucket.com/albums/ae151/energizzzer/photo-8.jpg

[svginferno]

Those are stock E60 wheels (5-Series).

[easymoney]

Look in the back of the wheel and you will find "BMW" and the part number.