If you are moving from Window to Window, or Mac to Mac, you can just copy the entire iTunes media library from one computer to the other.
Go ahead and set up the new iTunes on your computer. Locate where the it put the iTunes library by default. Now copy the old iTunes library to the new location. When you start iTunes on the new computer it should find and load the library. You'll then have to authorize the computer. Go to the Store menu and choose Authorize Computer.
I'm not sure how the iPad will act when it is connected to the new computer and iTunes. It may insist on being over written.
So, before you copy the library over, be sure you have a good sync on the old computer. Also right click on the iPad under devices and choose Transfer Purchases. That way if the new computer insists on over writing the iPad, at least it will just be an inconvenience time wise. You won't lose any of your media.
Do a backup too. This won't move with the iTunes media library, but if something goes drastically wrong you'll at least be able to start again from scratch with the old computer.
When you are done, and are sure everything is working properly on the new computer, be sure to go into iTunes on the old one and de-authorize it if you'll no longer be using iTunes on it. You can only authorize 5 computers with an iTunes account, so you don't want an old one taking up a slot.
How you actually move the file depends on what you've got available and how big it is. If it's large, then you'll want to use and external hard drive. Smaller libraries could be moved over your home network from or two a shared folder.
I looked for a good set of instructions on the web, but while I could follow them, more or less, none of them inspired me with enough confidence to pass on. So my final advice is just to give it a try. Just don't do anything permanent to the original iTunes until you are happy with how the new computer is working.
Finally, before you hook up your iPad to the new computer, go into iTunes Preferences. Under Devices check the box the prevents your devices from automatically syncing. That will give you the opportunity to go through all the sync settings when you hook up your iPad, before it tries to auto-sync and possible remove or add stuff you want left alone.