Help getting my old purchases into my newer computer library.

I had all my music on my iTunes on my old computer, and transerferred it to my iPad and iPhone4. Recently I had to update the software on my iPhone, and it deleted all my music. I knew it was going to do that, but I wasn't worried, becsuse I *thought* I could transfer them from my library.

When I went into iTUnes on my new computer, there is only like 2 purchases out of 200 listed, even if I look in past purchases. If I boot up the old computer, I can see all the purchases....(yes it is the same Apple ID).

I tried to sync the iPhone to the old computer. but it says I have to update the iTunes software, and when I try to do it automattically, it tells me it can't connect to the internet. (I'm typing this from the old computer, so it does have an internet connection.) I think if I reinstall iTunes, it's going to erase all my old purchases (Why aren' t they in the library anyway?)

I have also tried transferring from my iPad (which has the old library) with no luck. I cannot figure out how to do it. The iPad, also needs to be updated, but I don't want to do that until I can reclaim the music. I have "backed" up the iPad, on the computer, an *** says, it backed up...but when I physcially look for the back up, I cannot locate it.

I need help, I want to get my old library back on my iPhone and updated properly on my new computer. Any insight?