First Microsoft used warnings and migration tools to help make Windows XP users upgrade. Now, it's trying a different tack: bribery. In an effort to get folks to stop using the 12-year-old OS, Microsoft is offering XP hold-outs a $100 discount off new Windows 8 PCs. That sounds like a sweet deal -- and it might well be -- but there are several catches you should be aware of. First off, the promotion only applies to a select few models, and you'll need to visit a Microsoft Store to even see the full list.