I have found this tip and thought that is worth sharing
http://www.theipadguru.com/2010/05/18/guru-guide-sync-your-ipad-with-multiple-computers/
there you can see how they manage to hook the ipad to more than 1 computer. Tried that one on mine and it work as well.
From the dawn of the iPod, it seems that it has been Apples mission to ensure that your device is tied to one computer and one computer only. To say that this is annoying and impractical is making a huge understatement. If you own a device, the machine that its being hooked up to and the content that youre transferring, why are you limited to just linking that device and computer once? Well the point comes down to money. The record labels providing the music would love to see users confined to using and sharing music according to their rules, usually rules that involve them making the most money.
Too bad its so easy to just ignore all of that and do it anyway
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This guide is set up to allow you to do two simple things, one, get the iTunes ID of your computer, something that iTunes and your device use to verify that they are mated so that they can communicate properly. Then, we take that ID and apply it to the other computer that you want to use your device with. This is most ideal for situations where you want to sync your iPad with say a laptop and desktop that have different music on them. For instance, if I wanted to listen to some Sugarland or Rascal Flats (not likely), I would need to mosey on over to my wifes library and get them out of there. Cant do this if the other computers iTunes wants to wipe my device and overwrite it with neuvo-country (shudder). So, heres how we go about this
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Start here if you have a PCiPad, move on to the Mac Method section if you have a Mac
Windows Vista Method
First download HexEdit, youre going to need it.
Navigate to your Music folder, then the iTunes folder
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Right click the file named iTunes Music Library.xml, choose open with and Notepad.
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Copy the Library Persistent ID key and paste it into a text file or write it down. It should look something like 456e20293961CBA4. Do not save your changes!
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OK, time to move on to your second computer, the one you want to sync to in addition to your primary.
Lets back up iTunes Music Library.xml and iTunes Library.itl before we go mucking about with them. Go to Music>iTunes, select the two files and press ctrl+c and ctrl+v to create copies of the files.
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Right click on your iTunes Music Library.xml and select open with, Notepad to open it.
Find the same Library Persistent ID key, write this one down just in case, and replace it with the one you copied from your primary computer. Make sure you type it exactly right.
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Now open up the HexEdit program you downloaded at the beginning, you did download it right? Now open iTunes Library.itl in HexEdit.
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Hit Find in HexEdit and select Hex as the Find type. Then type in the original Library Persistent ID and hit OK.
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Once you find it, replace it with the new Persistent ID from your main computer, type it exactly in pairs of numbers to replace the original. Do it exactly or you will screw up your iTunes library file
but this is why we made backups! You didnt skip that step did you? Of course not.
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Now open iTunes, plug in your iPad and click Manually Manage music and videos. Notice no annoying erase your iPad message? Proceed to manage music to your hearts content from either machine!
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Mac Method
Were going to need HexEdit, make sure you get it from here.
Press Command Spacebar and type in iTunes. Scroll down to the folder that says iTunes Music, not iTunes Music and hit enter.
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Double click the file named iTunes Music Library.xml to open it in TextEdit.
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Write down the value of the Library Persistent ID key. Take care not to modify the file before closing. It should look something like A4E3DEFD1E51FF94.
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Now go to your second machine and repeat the above steps, once you have your iTunes folder open however, make sure to select both iTunes Library and iTunes Music Libraby.xml and press Command+c then Command+v to make copies for backup first.
Now double click to open iTunes Music Library.xml.
Change the Library Persistent ID key to the one from your main computer and save the file.
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Now, use HexEdit, you got that above right? Open the iTunes Library file in HexEdit. Once you have opened iTunes Library use HexEdit to search for the old Library Persistent ID we replaced in Step Five. Do this by clicking Find from the Menubar. Make sure to select Hex as your search type.
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Once found replace the old Library Persistent ID with the one from your main machine and save the file.
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You can now launch iTunes and connect your iPadiPad to the new computer for syncing, feel free to select Manually manage music and videos and manage away on either machine!
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