I need to transfer music from old itunes to iphone

I recently got the new iphone5, and need to download music onto it. Instead of downloading 1000+ songs I was going to just download my sister's music onto my phone. But, when I plugged in my phone to her computer, iTunes would not accept it. My sister won't download the new iTunes because she's afraid it won't let her download more music/apps onto her iPod since it's a very, very old generation. Is there anything I can do? Is this actually true?

I'm sure it's fine to download the new iTunes. My sister has the first generation iPod touch and it works fine with the new iTunes. There hasn't been any errors with it and she was able to put the music from iTunes onto her iPod. And when you say that your iPhone isn't being accepted, do you mean iTunes doesn't recognize that you plugged it in? Because if you are, try using a different cord.