My advice is don't! Doubletake is one of the most buggy pieces of software I have ever used. We purchased it about 5 years ago and I've worked with several versions but they just seem to get more broken with each release. We stopped renewing all of our licenses this year. One of their support guys even told me the latest release (this was in 2012) was rubbish and then used a hidden startup hack to get the old management console to work.
That said it might work well enough if you're running it on a local network and not a WAN as we were.