Recover postgreSQL databases from raw physical files

This is possible, you just need to copy the "data" folder (inside the Postgres installation folder) from the old computer to the new one, but there are a few things to keep in mind.

First, before you copy the files, you must stop the Postgres server service. So, Control Panel->Administrative tools->Services, find Postgres service and stop it. When you're done copying the files and setting permissions, start it again.

Second, you need to set the permissions for the data files. Because postgres server actually runs on another user account, it will not be able to access the files if you just copy them into the data folder, because it will not have permissions to do so. So you need to change the ownership of the files to the "postgres" user. I had to use subinacl for this, install it first, and then use it from command prompt like this (first navigate to folder where you installed it):

subinacl /subdirectories "C:\Program Files\PostgreSQL\8.2\data\*" /setowner=postgres

(Changing ownership should also be possible to do from the explorer: first you must disable "Use simple file sharing" in Folder options, then a "Security" tab will appear in the folder Properties dialog, and there are options there to set permissions and change ownership, but I wasn't able to do it that way.)

Now, if the server service can't start after you start it manually again, you can usually see the reason in the Event viewer (Administrative tools->Event viewer). Postgres will throw an error event, and inspecting it will give you a clue about what the problem is (sometimes it will complain about a postmaster.pid file, just remove it, etc.).

If you have the whole data folder, you have everything you need (as long as architecture is the same). Just try restoring it on another machine before wiping this one out, in case you didn't copy something.

Just save the data directory to disk. When launching Postgres, set the parameter telling it where the data directory is (see: wiki.postgresql.org). Or remove original data directory of the fresh installation and place the copy in its place.