I am trying to install ssh2 on xampp
Until now I have use
A couple of things you may have missed :-
Having a look here for the download there is only a 32bit version of SSH2 compiled with VC9 available for PHP5.4, so you will have to ensure you have the 32bit version of XAMPP installed.
Oh and a final note, you do not need, and should not do, the copy of php_ssh2.dll into the c:\windows\system32 so remove the dll from this folder. PHP knows where to load its extensions from and putting files in c:\windows\system32 will only confuse things when you want to upgrade your version of XAMPP.