as sebastian said, you need to download and install the source package first
next: open the vbproj file in notepad, and make sure the iis urls point to the specific url of your development instance.
next, open the sln file in visual studio (it is still vs2005, so if you are using vs2008, you are asked to upgrade the package)
NB: if you decide to make changes, it would be wise to change the modulename, namespaces, and the name of the dll's you are compiling to, otherwise, if anyone decides to upgrade to a future version of the module, he might get into quite some trouble