How do I install windows 7 onto my htc pro touch 2?

So windows 7 won’t run on your phone, certainly not in any way that might be useable.

If you mean windows phone 7 then I’m pretty sure microsoft dont allow older versions upgrade to it and your phones CPU anf touch screen doesn’t meet the minimum requirements for WP7 anyway. If you want windows phone 7 then you need a new phone.

Flash the rom , test see if it works . If your phone fails to meet minimum specs , get a new mobile