How do I imessage someone from my ipod touch to theirs?

No you need to ensure you've signed in with a valid Apple ID in iMessage settings. Go to settings-messages and ensure you're signed in. Once signed in, open messages and click the compose icon (top right) and type the address of your friends apple ID or telephone number (that has iOS 5 or newer) and then compose a message and send it. You will know it is ready to work/send when the "send" button turns blue.

No I believe you stated your question clearly, I mentioned you could send to a telephone number so you knew that you could, not because I wasn't certain what type of device you were sending an iMessage to.

Hopefully you've got it sorted though.

I already provided you with the instructions, and you marked it as the "correct answer".

If you are still unable to imessage ensure that BOTH you and your friend are on iOS 5 or newer. You are BOTH signed in with VALID Apple IDs (as described above). You BOTH need an active internet connection. Outside of that I can't think of anything preventing it from working.

He must sign in to imessage with a VALID Apple ID. First, his email address could be a valid Apple ID, and you could if he signs in messages with it. Second, if he chooses to use a different Apple ID you need to iMessage him at that ID. You can create a contact for him and just select his name/contact to message and don't need to worry what address you're using once it is saved.

I am not sure why he isn't able to sign in with his Apple ID and message you that way. Apple IDs are free, and he can create one here https://appleid.apple.com

You're welcome, hopefully you're able to get everything working.