You can go about this two ways; First you could simply copy the wallet.dat and put in in a safe place which you can later on transfer to your new hard drive, for example you USB. Secondly, you could note down on a piece of paper, or what ever and put them in a safe place. When it comes to restoring your wallet, you could create a new and import the private keys.

I would recommend just making a copy of the wallet.dat for the transfer, but still note down your private keys and keep them in a safe etc just in case one day you do forget your password for the client.