ok, the installation of pawtucket is much easier as i thought. I will write down some short instructions, which should help newbies like me ;-)

you should install CollectiveAccess (CA) with this instructions: http://wiki.collectiveaccess.org/index.php?title=Installation_(Providence)
download the packages of pawtucket via svn, you can save it in a subfolder of CA (SVN: http://collectiveaccess.svn.whirl-i-gig.com/CollectiveAccess/frontends/Pawtucket/trunk.)
Copy the setup.php-dist file (in the directory of pawtucket) to a file named setup.php
edit the setup.php in the same way like you have done it with the setup.php of CA, the only difference should be the value of "CA_URL_ROOT", here you have to fill in the direction to the subfolder of pawtucket. Note: you have to use the same php-database like in CA and also the same login etc.
open your webbrowser and go to the subdirectory of pawtucket. (If your login to CA is http://localhost/trunk/ then your access to pawtucket should be http://localhost/trunk/trunk/)
Thats it, there is no installer for pawtuckt, it should run directly

Note: There is no warranty for this instructions and Im not a native American/English speaker, but I hope this instructions can help you.

Good luck!