F19 --> F18 feasible?

[Beartooth]

My old Thinkpad T30 (on which I ran fedup from F18 to F19) is
beginning to seem like more effort than it's worth, even if eventual
success of the effort were a sure thing. Is there a FedDown lurking out
there somewhere?

Will an install DVD for F18 (preferably one with gnome as well as
xfce4) let me treat the installation as if it were an upgrade, and
preserve my data and tweaks?

Failing both of the above, does anyone have any experience
running CentOS on a T30 or comparable?