Since Apple likes to lump "Windows" and "PCs" together as the same thing, allow me to list the things that Apple has "stolen" from PCs:
PCI - PCI was first released in 1993. Apple adopted it in 1995.
IDE - IDE (Integrated Drive Electronics) became an ANSI standard in 1994. Apple adopted it in 1998. Previously, they used a proprietary version of SCSI.
USB - USB was first released in 1995. Apple adopted it in 1998. Before that, they used Firewire.
x86 processors - "PCs", referring to computers that are binary/hardware compatible with the original IBM PC, have been using Intel-compatible processors since 1981. Apple announced a change to Intel processors in 2005, and all Macs had them by 2006. Previously, they used PowerPC processors, and before that, Motorola 68ks.
Apple: A history of innovatively playing "catch-up", and then claiming their hardware is the most "advanced."
And, since we were talking about what Microsoft stole from OS X, lets talk about what Apple MUST have copied, since Microsoft had it first:
Pre-emptive multi-tasking - In layman's terms, it means the operating system can run more than one task at once, and both programs can use resources to complete the task. Otherwise, one has to wait for the task with a higher priority to finish first before it can continue working. Windows has been able to do that since Windows 95. Macs have been unable to do that until Mac OS X Server, released in 1999.
Right-clicking - Windows has supported right-clicking since the very beginning. Macs did not support right-clicking officially until OS X. To this day, even though the operating system can support two or three-button mice, Apple still ships mice with only one button. If you mention this to a Mac user, they will say "Just buy a three-button mouse", and then continue to tell you how awesome their computers are.
Bundling Internet Explorer - Windows has bundled Internet Explorer since the first CD release of Windows 95. Here is a funny video of Steve Jobs kissing Microsofts' ***, praising Internet Explorer, in 1997.
http://www.youtube.com/watch?v=WxOp5mBY9IY