WINE is not an Emulator!
When users think of an emulator, they tend to think of things like game console emulators or virtualization software. This is the wrong way to think about Wine - Wine runs Windows applications in essentially the same way Windows does. Wine is just a native Unix substitute for the components of Windows; there is no inherent loss of speed due to "emulation" when using Wine, nor is there a need to open Wine before running your application.
That said, Wine can be thought of as a Windows emulator in much the same way that Windows Vista can be thought of as a Windows XP emulator; both allow you to run the same applications by translating system calls in much the same way. Setting Wine to mimic Windows XP is not much different from setting Vista to launch an application in XP compatibility mode.