Running out of space on Raid 5

I have a Dell 2600 with three 36 GB SCSI 15 rpm drives with drive c: only set at 5.85 gb and d: at 61.8 gb. The Small Bus Server 2003 OS is on C: and with all the hotfix updates the drive is now full. I have moved everything to the D: drive that I can. I use this server in a small office for a SQL medical office management system.
Is there any way I can move things around? I have enough experience to have installed the original NT4 system and upgrade to 2003 almost 2 years ago but I am not by any means an IT guy…