The user that is installing Mac OS X must agree to the license before installing the operating system. According to the license the software can only be installed on a «Single Apple-labeled computer» at a time.
2. Permitted License Uses and Restrictions.
A. This License allows you to install and use one copy of the Apple Software on a single Apple-labeled computer at a time. This License does not allow the Apple Software to exist on more than one computer at a time, and you may not make the Apple Software available over a network where it could be used by multiple computers at the same time. You may make one copy of the Apple Software (excluding the Boot ROM code) in machine-readable form for backup purposes only; provided that the backup copy must include all copyright or other proprietary notices contained on the original.
The definition of a label could be called into question. By applying an Apple sticker to the external case of the PC it could be argued that you are meeting the usage clause. The license use does not state a requirement for an official Apple label with an Apple Hardware Serial number.
А наклеечки-то у меня есть :-)