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Parallels

If your needs are less sophisticated, like mine, Parallels should do the trick. I got version 2.0 and it's been great. Since upgrading to Leopard, I even copied everything over onto the new hardrive I got via time machine and it's still great. One problem though, I play the old game star craft, and was not satisfied with it's performance, so I always use boot camp to play it on (since it crashes on OS X). I love Coherence.
 
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