The key difference is between Virtualised and Native OSs
I own an early 2011 Macbook pro. The reason I bought it is because I wanted to play the withcer 1 & 2 and Diablo 2 & 3. Those were the 4 games that I plan to play on it. The witcher is A windows only game so I was going to install windows 7. But then I read on this forum that it slowed peoples computers down a lot.
Does anyone know if this is true & if I'm going to have trouble running the witcher and witcher 2 on my mac using windows through bootcamp?
It's probably people trying to run Windows 7 Ultimate in emulation (via Parallels, VMware Fusion, VirtualBox, etc.) on older Macs that just aren't up to spec.
Bear in mind that a Mac running Windows is essentially just another PC, and so the minimum hardware specifications for any particular version of Windows will be the same. If you try to emulate Windows 7 on a Mac that only has the minimum requirements for that one OS, then sharing capability between Win7 & OSX will mean that both are underpowered.
However, BootCamp is not an emulator; it's a combination of an extension to Disk Utility that creates a NTFS partition on your Mac's main boot drive for installing Windows on, and the "Bootcamp.exe" App to run in Windows once you've installed it - the App adds the option to pick the primary boot partition in the Windows control panel, and installs all the drivers for any multi-touch or Apple-specific Bluetooth input devices, iSight/FaceTime camera, etc.
Once that's done, then you'll have probably the best PC there is! Windows, but with custom Mac-hardware drivers (ported directly from OSX's own bespoke Kexts) - and with the option to switch between them just by holding-down the Option key when you reboot.