You always wanted to play with Asterisk but Linux scares you? If you are a newcomer into VoIP world or just a Windows lover then you may start your PBX experiences with Axon Virtual PBX Software, a free product from NCH Swift Sound http://www.nch.com.au/
Installation is just 1 minute away from the download. To test the PBX you may also want to install a few SIP clients such as Express Talk from the same company or X-Lite from CounterPath (http://www.xten.net/). If you already have a hard phone or an ATA you may connect those as well to your newly installed software.