Is it looking for CS4? Can you try deactivating the CS4 on your old computer, install CS4 on your new computer, activate it, and then install CS5? Maybe you want to wait for someone on this forum for a better answer. Before upgrading you might want to take care of items mentioned in this article http://prairiefireproductions.com/2010/04/a-protocol-for-upgrading-to-adobe-photoshop-cs5/
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