As i version my apps, I create a zip file of the previous version and store it on a secondary drive and can unzip a previous version if need be.
Something to note in the way of web applications, you typically will want to restore a previous version of an application to a different directory so that you don't overwrite your current application and, in this case, you will have to edit the .sln file after you have unzipped everything.
Say that the original path to your app was //servername/workingdirectory and you unzip to //servername/oldversion, if you try to open the project Visual Studio it will give you an error saying that it cant resolve the server, yadda yadda yadda.
Open your .sln file and, if memory serves me, the first line will have the path of the application; change this line to reflect the new path to your application and you should be good to go.
"The one language all programmers understand is profanity."