Hmmm.
This sounds like you are going to have to create a component or, if you have access to the server, you could rigth a Windows Scripting Host file (WSH) that will unzip files in X directory. (WSH files can be written in VBScript)
http://www.codecomments.com/VBScript/message731969.html
That will point you in the right direction as far as WSH goes but doing this directly from a pure .NET page, I don't think you are going to be able to do that. (You can shell cmd.exe from an asp.net page and send commands to it, telling it to execute a .bat file for instance which could also be an option for you.)
I am going to post this in here just because its the Beginners forum: When you shell cmd.exe from a .NET page the user wont see the command window so you dont have to worry about them free forming something in like deltree. ;]
HtH
"The one language all programmers understand is profanity."