Hidden folder in /Users/Shared that has MD5-encrypted name of another user I was familiarizing myself with some of the hidden files in OS X (while cleaning house) and I came across a hidden folder inside the /Users/Shared directory. It's name is "." followed by a 32-character hex string, which (I googled the string) is the MD5-encrypted version of the name of my user account on this computer.

The folder was created in 2008, but last modified just two days ago (which leads me to believe it's been accessed somewhat regularly). It contains three files: "." (4 KB document, created and modified two days ago), ".." (Zero KB document, created and modified in 2008), and "Temporary Items" (4 KB document, created and modified two days ago).

Is this normal, or is something strange going on? (Have I been hacked?) I'm using a PowerPC Mac running 10.4.11 (yeah, I know).
Your question appears to be slightly incomplete, however the first two files are standard unix "files".

. is the shortcut for the current directory;
.. is the shortcut for the directory up one in the tree.

A lot of Unix shells require you to completely specify the path to an executable when executing them from the command line, and an example you may have seen:

./Make


Is a request to execute the file Make in the current directory.

Similarly, using the command

cd ..


Is a request to change the directory to the parent of the current directory.

Your third file is not named in your question so I cannot provide an answer for that.