Resolved Question: Basic iPod Questions - I am looking at buying my first iPod?

For the past 3 years, I have had a 40gb Creative Zen Jukebox MP3 player which I have been happy with. Now I want to purchase an iPod due to accessories. My question - I have thousands of songs on my computer that did not come through iTunes. Can I load them on an iPod? I can put them on my Zen very easily, but they are not "coded" with iTunes security or whatever that is. Does this matter? I don't want to buy an iPod if I can't keep all of the music I already have. Surely there is a way around it. I have just never touched an iPod so I don't know if it works the same. Thanks in advance for your advice!