Problem with FC3 partition

[Franco]

Hi, i'm installing a fresh FC3 on an Athlon 1.8 with 512 MB of ram
and 2 HD, first 40GB and second 80 GB.
I need to create a boot partition on the first hd and the root on the
second hd but when i create it and install FC3 on the boot after 
hardware check it hang !!! If i do an FC3 default partition it work
fine but seams to do a virtual volume so the root is the sum of 2 hd,
but in this installation it an hd fails i will lose all data on other
hd?! Can someone help me to the right partition? Thanks in advance.
Frank.