I used the RH 7.1 RPMs with Mandrake 8.0.
To uninstall the postgres that comes with mandrake, go into "software manager" (on your desktop), find it, and tell the package manager to uninstall it. You're going to have to grab the libxml(??) rpm also, postgres drivers RPMs, etc etc. Jonathan Marsden has everything you need on his site, or did a couple months ago.
Good luck :)
Cathy Sarisky