Put Music on Xbox 360 with no PC Network Connection
"I am trying to get music from my PC to my Xbox 360. The problem is that my PC is an older model so it doesn't have an Ethernet port. Is there any way to do this?"
There are basically two ways to get music files from your PC to your Xbox 360. Option one is to use your home network. If your computer doesn't have an Ethernet port, this option is out unless you feel comfortable adding an Ethernet port. Option two is to use physically transport the files from your PC to your Xbox 360 using some kind of storage media.
Adding an Ethernet Port to Your PC
There are two ways you can add an Ethernet port to your PC. You can use the method that requires opening up the case and installing a card, which you might not be comfortable with, or you can purchase a USB to Ethernet adapter. Basically the USB Ethernet adapter connects to a USB port on your computer and makes it work as an Ethernet port. If you plan to go that route, it might be easier to simply get a USB wireless adapter instead, especially if you already have a wireless router.
Moving Files with Physical Media
Probably the easiest thing to do would be to use a USB thumb drive or external USB hard drive. Copy your music to the drive, connect it to a USB port on the Xbox 360 and you are ready to listen. The Xbox 360 can read music from almost any source except tracks purchased from iTunes with Fairplay DRM.