Alrighty, this will not cover any particular tools and assumes you are intelligent enough to figure out how to accomplish each given step 🙂
Summary: We will create a partition before we install to hold onto files, and then mount it later to retrieve them, without dual-booting.
1.)Pop in your livecd and run your favorite partitioner.
2.)Resize your old OS so you have enough freespace for your normal install+the space of the files you wish to keep.
3.)Create a new partition of ext4 or ext3 type and set it’s size to equal(or slightly more for safety) the size of all the files you wish to keep. Mount it on something like /backup or whatever
4.)Copy files over to the /backup
5.)Proceed to install, editing partitions manually to make sure everything runs smoothly(create a swap partition of 2x your ram, and the rest goes to your new OS with mountpoint /)
6.)If needed, place a mount point for the backups or just mount manually later, your choice.
7.)Proceed and blah blah blah wait for your system to restart.
8.)Mount the /backup partition(if needed) and then copy the files to their new destination.
8a.)In many cases this can include preferences such as FF profiles 🙂
9.)Unmount and delete the now useless partition, resize to take up the freed space.
There ya go! 🙂 It’s simple, but handy if you’ve ran out of CDs or whatever you use to backup files.