ok well you can download Trixbox and it will install Free Pbx and Asterisk for you. It creates an auto install CD and you just need a computer to put it on. It will wipe the PC.
You will need phones. You can use VOIP or legacy POTs phones if you want to connected them to an ATA (analog telephone adapter) using FXS (Foreign Exchange Service) ports.
If you are going to make the JUMP to VoIP get VoIP phones. You can get cheap ones at Voipsupply.com or many other vendors. They are as cheap as $50.
You can connect it to a phone line using an FXO (Foreign Exchange Office) port, again ATA's can have them also. The simplest way to do it is using a SIP service like Voice Pulse. For $11 a month you can purchase a SIP trunk. You get 4 connection (Calls at a time) and one phone number. You will only have to pay for outbound calls and it's a fraction of a cent per minute.
For full step by step instruction in installing Trixbox, setting it up and getting your IVR set up look at (
http://dumbme.mbit.com.au/trixbox/trixbox_without_tears.pdf).
Good luck