I believe you are talking about "Branding" a PC.

If so, then you need to find the Oemlogo.bmp and Oeminfo.ini, in the Windows/System or Windows/System32 folder.

Have a look at this site;

http://www.beemerworld.com/tips/systemproperties.htm

I would expect that such branding can only be done under licence from MIcrosoft.

Mark