Would it be possible to use an external USB case for the new 2.5" HD and plug that into the laptop?
Clone the internal laptop HD to the larger one in the USB case - using Acronis (for example).
Then put the new, larger, 2.5" HD inside the laptop.
Come on experts, does this make sense?
EDITED TO ADD: Note p*St # 123 on the Ultimate List of Free Software thread. It address lasernigel's question.