How would I install TH2? I have X3 producer

If your talking about TH2 Producer, run the installer for X3 and when it prompts you about custom installation, select that. Then pages will be brought up of what is included in the installation. Uncheck the ones you don't need to install again. Eventually, you will see TH2 Producer. Check that box. WARNING! I always double check to make sure that nothing else is set to install. When all is good, let it rip.
I do have to put in my 2 cents. TH2 Producer is very good but it doesn't have all the features of the full blown version. I used TH2 Producer and was pretty happy but sometimes felt cramped that it didn't have some stomp FX and the additional amp sims. I liked it enough to invest in full TH2. The Brunetti amps in that version have become my go to for guitar amps in the box! They are absolutely amazing!
That is a pretty dubious claim considering I have Guitar Rig, Amplitube, and the LE version of ReValver! I have been sitting on the fence for a while about getting S-Gear. Some people love it and some people don't.
I have played guitar in groups and on sessions for well over 40 years. I will tell you this about sims. The right one in the right song context can be a great time saver and blended in to a track correctly, no one will ever know the difference. On the other hand, don't expect the guitar to feel or respond to your hands the way a true amp does. The feel can be very stiff. Bends just feel like they are fighting you a little harder. Sound-wise, there is something that is almost unexplainable about the sound of a real mic on a real amp. The mic seems to capture the airiness around the amp. I have not found an amp sim yet that captures that aura for like of a better term. I do not tell you this to discourage you from installing or using a sim. I just think you should know, based on someone's opinion that actually uses this on almost a daily basis. If for no other reason you should install it just to have another option for your guitar sounds. I have even used TH2 plugged stereo straight in to the PA out on gigs with a midi foot controller. My guitar buddies laughed when I came in with a guitar and a laptop. After the first couple of tunes they were gathered around the screen of my little lappie with their mouths hanging open. I was the one laughing!
I hope this has been of use to you. Let us know how the install went on this thread and what you think of TH2 Producer.
BTW, if you want to see technology and guitars gone insane check YouTube for a Rig Rundown of Vernon Reid's stage rig. INSANE!