I'm the author of the Wiki article to which you are referring so am very familiar with it. It sounds like you are following those steps so I'm not sure what if any steps you are missing.
What are the types errors that are shown when opening the .sln file in VS 2008? - Missing references? Missing namespaces? Obsolete (deprecated) methods?
On the possibility that your download of the source package was corrupted I'd suggest doing a new download from
http://dotnetnuke.codeplex./releases. Before extracting the .zip package into your installation folder be sure to right click on the downloaded package icon or filename, select "Properties" from the context menu, and if there is an "Unblock" button click on it.
After extracting the .zip package, be sure to rename release.config or development.config to web.config.
Am I correct that you have properly added a new application in IIS, have assigned it an alias and pointed that alias to the Website folder (not the root folder) of the extracted package? Are you using an ASP.Net 3.5 or ASP.Net 4.0 application pool? Have you granted full filesystem permissions on the Website folder (and all child folders) to the correct ASP.Net worker process account, i.e. the AppPool Identity user?
Make sure that you (before opening the .sln file in VS 2008) first open the .sln file in Notepad or other text editor and make the changes to the website project url as indicated in the yellow highlighted text in my first reply and as indicated in the Wiki.
After opening the solution file in VS 2008, open the Build --> Build Configuration Manager, select your desired Debug or Release configuration and make sure that all solution projects (EXCEPT the DotNetNuke_Community website project) are checked. Then Build the solution.