If you use the search function you'll see I think maybe 2 more threads and they have an abundance of info. I have 2 gauges in my car with a 3rd in the plans. i have my boost gauge, a nitrous gauge, and I plan to get an oil pressure gauge. I have mine mounted on the A pillar using a custom triple mount I had made a while back.
I did what the others suggested and tapped into the vacuum line on the throttle body and it works perfectly. The pain is routing the boost tubing from your vacuum line all the way to wherever you put your gauge.