I installed 3.51 and I see no signs that it is there! Where should I look?

Yes.

When I click on the IP icon below postbit (thread view) it shows this:

$postinfo[username]'s information stored for post: $postinfo[postid]
IP Address : $postinfo[ipaddress].
Host Address : $postinfo[hostaddress].
Alt IP Address : $postinfo[altip].
Alt Host Address : $postinfo[althostaddress].
User Agent : $postinfo[useragent].

How do I correct this?

I have no idea since that display is not part of this hack.

I find on my board it shows EVERY users IP as a proxy

The Real IP Address is: **.**.*.***
user-1765.l1.c3.dsl.pol.co.uk
The Proxy Server IP Address is: PROXYIP

Then you have done something wrong, or more likely not done something (i.e. the file edits to class_core).

I did the file edit 5 times :[

and uploaded them ?

I can;t tell if it is working. I don't have any errors, I don't get that px.gif anywhere on any style i use, and i uploaded the px.gif to all the style button folders. I click on the ip address on one of the members post but it shows the standard ip addy.

You won't see any difference unless someone posts via a detected proxy.