As above, hard drive caddy with your old drive, or, do what I did and buy a NAT drive (stand alone drive that plugs into a spare ethernet port on your broadband router) which means you can copy all your files including itunes onto it, and then you can copy stuff back to the new laptop as and when you want it.
Its a little slow as its limited by the network, but, you get a backup of all your files, easy to backup in the future, and you don’t need to copy everything to the new lappy for the sake of not losing it. You can just copy what you want, rather than fill the drive with 6 years of junk.
Advantages over a portable drive, is you don’t need to go and find it each time you want to use it, and it can’t get knocked off the arm of the sofa, (like I did) potentially losing your backed up files. The one I’ve got (Western Digital Mybook) is compatible with itunes and can act as a central server thing, but I’ve never really bothered as I rarely play music from my laptop.
P.S. A normal ethernet cable won’t work directly between laptops will it? I thought it needed to be wired slightly differently, making it a null cable?