MasterVB.NET

Hi ,
I have written a program to zip files with Shell32 in C#.
The program zips the folders and then deletes the original folders.
The problem is that the folders are big in size ,each being atleast 10MB in size.
Now when the program starts the delete process it gives me that the folder cannot be deleted because it is being used by other process.
Now I think that the zip process is not completed and the delete process starts and hence the error.
Is there any way to know that the folders are not being used anymore and then i can proceed with the delete operation.
Or is there anything that will tell me that the zip prcess is over.
I am using the thread.sleep method but it aint helping.

Thanks