wine is fairly efficient for that reason. It doesn't
emulate anything, it just provides the environment required by peecee
programs to enable them to run in a unix environment. It's a really neat
hack, actually.

Although wine is not perfect, there are a number of microsoft windows
programs that run quite nicely on linux or mac with wine. I use
codeweavers crossover office, a commercially supported version of wine,
to run visio at work. Best $39 I ever spent.