Adding Hard drive(s) to a DL380 G3

[CA1293436]

Sorry for the newbie question, but I'm not that familiar with everything having to with creating a RAID.
I have a DL380 G3 server that I just got put in charge of. It only has one 72gig drive in it. It has 3 partitions. C:(OS) is 9Gb, E:(APPS) is 45Gb, and F:(USERs) is 15Gb. Well, the E: & F: drive have almost filled up. What is the best way to increase the disk space with out having to loose everything/anything or doing a restore? This server also has on it : DNS, DHCP, and is the only DC/GC in it's domain. I know, not smooth, but that's what I have been given.

Obviously, there is no redundancy there now, but I would like to resolve that with creating some sort of RAID. What is the best solution. I have ordered two DL360 G4's to put in place for DNS, DHCP, and DCs/GCs in this domain. So this DL380 will just basically become a F/P server. Thank you.