In some respects, it really is that easy. Installing Windows XP on a Mac with an Intel CPU can be done through Apple's free Boot Camp utility, which creates a separate partition on your hard drive where XP lives. It's a fairly simple procedure, and you end up with a dual-boot system. Another option is Parallels Desktop for Mac, which runs XP though the Mac OS.
There are, however, a few important differences that longtime Windows users should watch out for when considering the switch to Apple hardware. The most obvious is the lack of a right mouse button. Laptops such as the MacBook have only a single mouse button, and when running Windows, figuring out how to right-click will be your first major challenge.
Fortunately, there are several solutions. The simplest is to plug in a two-button USB mouse. But since that's not always convenient, there are several software apps that will help. Apple Mouse Utility is a simple app that lets you hold CTRL while clicking the single mouse button for a right click, while Input Remapper has a more extensive list of remapped buttons, including a Windows Delete key (Mac keyboards have a Delete key, but it's the Windows equivalent of Backspace). If you don't want to install any third-party software, Shift-F10 with bring up the contextual menu for any highlighted icon or file.
One last helpful hint: If you miss the dedicated scroll bar found on the touch pads of most Windows laptops, try giving your MacBook the old two-finger salute: simply run two fingers down the touch pad, and the page will scroll.