Easy one, when you have the Mint live cd booted and on the Mint desktop, you should see an icon on that desktop labelled "Install" - double click on that to run the install procedure and follow the instruction. When you get to the disk partition section just choose "use entire disk" (assuming you dont need that horrible Win7 thing
). Carry on the install and you should have a nice minty machine
Just make sure you have all your files off it first - you seem to indicate you have done this though.