these are the things that I used to do when I first started.
- Have routine for starting work - something like always starting at some defined time. I used to walk to the local shop and buy a newspaper.
- I made sure that I went out at lunchtimes and breaks and talked to people in the neighbourhood.
- I occasionally made a point of visiting local pubs/restaurants at the time other businesses kicked out so that I would meet people working locally. This sort of simulated "grabbing a few after work with the colleagues".
The point was that I would be lonely during work, but I'd mitigate it by interacting with people every day. These days I use IM and make sure I have non work & work related conversations with colleagues too.
An important thing to remember is that you are working, so you need to focus. If you're clever you can use the isolation to help you focus on the work better. This means that you may be more effective but at the same time you have to watch for mental fatigue and a good way to combat is to follow the steps above.
These days are lots of things that are accessible via the internet such as meetup.com where you can get together with people for professional or non professional networking. One person I met like this a fellow programmer who lived locally and we used to code review for each other.