While it isn't necessarily super complicated to set up a computer to host a website it isn't exactly something a "Dummies" book can walk you through. There are a lot of implications to running a site on your own hardware and software including, but not limited to, security, proper configuration, etc. I *do* have a couple of my own servers that I run myself (one at my house for personal and "development" stuff, one at my brother's house for other personal stuff but higher traffic). The computer at my house is a Celeron 2ghz w/1GB RAM, 80GB HD and it runs just fine. The computer I store at my brother's house is an older Xeon (2ghz I think) w/1.5GB RAM, 160GB HD (SATA) + 30GB HD (SCSI)... and it runs QUITE well.
However back to the question... if you don't have a lot of experience configuring websites, it might not be a good idea. Not saying it can't be done, everybody starts somewhere... but you might save yourself a lot of headache and time going with a host such as 3Essentials or others. Even with having two of my own servers I still host some more critical websites with a 3rd party.
Lastly -- DNN would work just dandy for your needs and it does have a learning curve initially but a Dummies book or something like that should help you get going.
Good luck and if you have more questions or need for help, the forums here are a great place to look or you could contact people like me, Mitchel Sellers, etc and get more personal help.