Miui Captivate

3 Button Recovery   

1. Turn off phone
2. Hold all three buttons (both up and down volume buttons; power button)
3. Hold them, the at&t boot screen will show up.  Hold them for about a second after the at&t screen comes up and release.
4. If your phone goes into the recovery menu then your 3 button fix is working properly and you can flash MIUI.
5. To reboot phone, just scroll to where it says "reboot system now" with your volume rocker and select it with the power button.