In my May 25th post I forgot to add one of the most important tools you'll need - a good virtual machine environent.
There are three to choose from...
Once you have built a DC/application server and a client or two you have the perfect safe environment to experiment in. If it all goes horribly wrong you can roll back the changes you have made and start again.
My preference is for Virtual PC 2007 or VMWare Workstation. They both run as simple applications. Virtual Server installs and is managed through a web site and is a whole lot more fiddly to use.
Both of the Microsoft products are free but VMWare is still the better product.