I resize the RH partition with the Mandrake installation tool but RH dont start any more. Just Mandrake 9.0 and XinXP.
That was probably caused by Mandrake's installer overwriting the bootloader. This could happen again when you install Mandrake, but all you have to do is make an entry in the bootloader for your RH installation. Before you install Mandrake, copy your lilo.conf to your /home directory. After booting into Mandrake, you can copy the applicable RH lines from your old lilo.conf to your new one, and you should be OK. You would then need to copy the newly completed lilo.conf to your RH /etc as well, so that you can make changes to the bootloader from RH if you want to.