Question about adding disks to MD1000

Hi, I'm new to this forum and to using Dell PowerVaults, so excuse me if this question is a bit too novice: I have an MD1000 attached to a Dell PowerEdge 1850 running RHEL 4. The MD1000 has 3 drives configured as RAID5 and is seen by the OS as a single LVM Volume Group. I need to add additional drives to the MD1000 so I can increase the size of this volume group. What I don't know is whether or not I can do this "on the fly." Has anyone done something like this before who can tell me how it's done? Thanks!