So this was my father's bitcointalk account. There's also wallet.dat and a text file:

bitcoin.org
bitcointalk.org
The password is THE DATE
13zEUPdpCDT3JGqv4o61vXQpgWWdxMEZeX

The coins are still there. I guess I can try some dates

I've never used the old Bitcoin client. What do I do?