It’s a lot easier to rename the “old” volume group if the old drive is the only one connected to the system.
Using your first FC4 installation CD and with only the old drive installed, boot into rescue mode (boot: linux rescue), but don’t search for or mount the FC installation. At the command prompt, you will probably need to active the lvm like this:
lvm vgchange -a y
The last two commands should list your volume group(s) and logical volume(s). Now use vgrename to fix the problem:
lvm vgrename VolGroup00 whatever_you_want_to_call_it
Note that all lvm commands need to be preceded with “lvm” in rescue mode.
via Two LVM VolGroup’s, same name, one is system disk – what to do?.