Sold Computer, Need to Backup Data

prety much. might want to back up your application folder as well
theres a program "carbon copy cloner" or something
that might be of use to you. ( i havnt used it )

 

if you have a firewire drive you can clone your boot disk using Carbon Copy Cloner if not you will need to burn your user directory to DVD-rom / CD.
I would recommend that you do regular backup to a FW disk & burn stuff to DVD-rom as you go, If you have a disk fail you will lose the lot.!
Also you might want to do a clean install of osx & do a zero all data format, this will get rid of any personal stuff you might not want the person buying your machine to find.