The server will be down tomorrow morning starting at 9:00 AM CST. That time of morning is usually dead, so that's when I decided to do it. The server will remain down while I install a second harddrive and format this one and setup a RAID-0 between the two drives. I predict this may take no more than an hour. After that the server will be up, but may experience reboots as I reinstall my favorite programs. I'll time these reboots during inactive periods.
This will result in double harddrive capacity (from 40 to 80 gigs) and, because of the RAID, harddrive access times will be cut in half.
Of course, there's a possibility that it may not occur tomorrow if my boss decides to be a bitch and make me work all day.