In order to install a PeopleSoft application, we need to choose a database.
Oracle seems a good choice, even if the development was (still is ?) in most of case on SQL Server...
Then Tuxedo, and a webserver like Weblogic.
The choice of PeopleTools version, actually the last version is 8.48 (new from July), can be deciding what you can, and how many time your application can live without a big upgrade.
You can download all softwares (main version, not upgrade) on http://edelivery.oracle.com/ (unfortunately a http server, so download can be long) and patches on the ftp server ftp.peoplesoft.com (anonymous user).
I advise the reading of the white paper PeopleSoft Enterprise Architecture for more understanding.