LinuxQuestions.org - Server with low energy use and personal file storage

So I am thinking about getting something that is cheaper energy wise and would like some recommendations.

Here is what I have right now (I picked this up for $30 just to test the waters):
Dell Precision 670, 650 W power supply, Xeon Processor, 2GB RAM
Has SCSI Raid 0 & 1
Has SATA 1.5 Raid 0 & 1

I liked the idea of putting the OS and webpages on the SCSI, having it on a RAID in case of failure and putting my less accessed, more numerous files on the larger SATA drives. But is there a better, newer, smaller, cheaper way?

What will my server be used for? It will serve files to family members as we organize pictures, music, etc. Maybe 5-10 people may have access via SSH. It will also serve as a wiki for organizing some research projects using mediawiki, again 5-10 people. I will also be using it for my own personal web development projects. 95% of the activity for the machine will hopefully take place remotely, that last 5% will just be me backing up the machine locally and for other maintenance items, hard drive failures... :-(

So what am I asking for in general? How much does it cost to run a personal server, electricity wise, per month? Also, does anyone have a cheaper recommendation then this Dell that will give me a reliable

PS: I'm a newbie at this, so there may be dedicated server options that may solve my problems, but I like the challenge of building this server and having my own little space on the internet to do things, 24/7. Plus I have learned a great deal over the past week, and would like to continue to learn more about linux.