Hmm. I'm not sure 50s songs are royalty free. I think I heard someone say Frank Sinatra's family still recieves royalties for his songs.

To anyone who's interested, here's the songs that will be in the map:
"I Don't Want to Set the World on Fire" -The Ink Spots
"Jeepers Creepers" -Paul Whiteman
"Mr. Sandman" -The Chordettes
"Civilization" -Danny Kaye and the Andrews Sisters
"Way Back Home" -Bob Crosby

Okay, thanks guys; the songs are already accredited to the makers of the songs, but I'll also make a note in the map download of their origin / artists.

Funny you mention "I Don't Want to Set the World on Fire" because the map is going to be named after it: "A World on Fire"

I'm going to assume you're taking such songs like 'I Don't Want to Set the World on Fire' and 'Mighty Man'. Bethesda doesn't have copyright/ownership of those songs if I'm not mistaken, seeing as they're not their own work. The songs in Fallout are borrowed from a lot of people, and seeing as the game tries for a vintage 50s feel, a lot of the songs are from that time period.

Something like an old forgotten song from the 50s isn't going to have much in the way of copyright I believe, they should be public domain by this time. I wouldn't worry too much about it. However, if you're going to distribute this pack online or whatever, I would do like Voxel says and make sure to acknowledge that the songs aren't yours and put credit where credit is due.

its not illegal to take songs from other artists and put it in your resource pack, but it is illegal to distribute the resource pack without acknowledging that the songs were not of your creation. If you keep the pack to yourself its fine, but I would redistribute it without permission first.