Difficulty transferring music to new computer despite following suggested steps

I followed the steps on the website for using an iPod to transfer music from an old mac to a new PC, but it only worked for the songs purchased over iTunes. How do I transfer the thousands of other songs to the new computer? The iPod is formatted for Windows. I was sucessful in activating the disk usage and copying everything to the spare space in the iPod, but the download to the new PC is sitting there working, saying it's done and then the new music is nowhere to be found. Help please?