you can make the second disk part of VolGroup00. To do that you need to do 3 things:
1) destroy the partition table on it
dd if=/dev/zero of=/dev/sdb bs=512 count=1
2) initialize it as an available physical volume
3) add the disk to the volume group
vgextend VolGroup00 /dev/sdb
that should do it. google lvm for more info and details.
edit: mind you, this will destroy all the current info on /dev/sdb. If you want to preserve it, you need to back it up. Then you can follow the steps above and then restore.