A song purchased from iTunes can be enabled to play on up to five computers, and an unlimited number of iPods. The latest version of the iPod/iTunes software allows iTunes music to be transferred between different computers via the iPod itself, IF both computers previously have been enabled to play music purchased by the iTunes account holder who bought the song.
Use your dial-up connection to make sure your own computer is enabled for use with your son's iTunes account. Make sure you have the most up-to-date iTunes and iPod software, and look for the "Transfer Purchases from iPod" command on the "File" menu. You might have to set the iPod to handle music transfers manually, as a previous response to your question mentioned, but I don't think this is true with the latest version of the software.
However, music that was copied from CD, stolen from eDonkey or LimeWire, or downloaded from other sources cannot be transferred in this way. And because the iPod keeps its music in hidden directories with cryptic file names, it is not the case that you can simply drag and drop the music files.
There are freeware and shareware programs, like iPod Music Liberator, that can see through the veil Apple cast over the music files on the iPod, and allow you to extract non-iTunes song files to your own computer. This works for us on the Mac, but I assume there are similar programs for the PC too.
bttt
Option #2 is a little more work, but you can simply mount the iPod as a hard drive, copy the files over as data, copy them off to your own HD, and then import into iTunes. At least until Vista blocks that.