If you want to try it out (I highly recommend it) then check out the post by Keith from PlannerWire on how to install it, How to Install and Use Tweet Old Post.
Tweet Old Post is one of my favorite plugins, always has been. There was a little glitch awhile back that caused me to uninstall it, but it is back in my good graces and I am ready to get it working for me and my client’s meeting and event websites.
What is Tweet Old Post
Tweet Old Post does exactly what its name suggests. For those working on the WordPress Platform, this amazing little plugin will send old posts out to your twitter followers.