If you opt for the manual partitioning option, you can select edit on the partition used for home. Don't format it. Just select /home as the mount point.

If you want to use the same username, I would recommend adding a suffix to your home directory. For example, for FC8, use /home/username-fc8, and for SuSE /home/username-suse, etc. You can do this when entering the the information for the intitial user during the installation. Or you could do this for the other distro's user's home directory ( sudo mv /home/username /home/username-fc8 ) and then edit the home directory field in /etc/password.

E.G. On my laptop I could:
sudo mv /home/jschiwal /home/jschiwal-suse
sudo sed -i '/jschiwal/s#home/jschiwal#home/jschiwal-suse#' passwd

Now after installing Fedore Core 8, I would have
/home/jschiwal-suse
/home/jschiwal

The latter from the FC8 install. I could similarily rename the directory and edit the FC's passwd file the same way.

Note that for the case of SuSE and Fedora Core 8, the range of UIDs for regular users are different.