asp.net vb creating a unique id for insert form

Hi,
We have a vb.net application within our office and we have recently been asked by a customer to facilitate the process of sending us data by providing an online portal whereby the information they send will be input directly in to our inhouse app (SQL server).

I have created an ASP.NET/VB application and created an input form. You dont need to log in or anything just navigate to the form, fill it in and then submit.
I have got the form working and once the required fields are completed you can click submit and my code uses an sql insert statement to input the data in to our sql server.

The problem is I also ask the user to upload several pictures. There are 4 tickboxes and when you tick each box there is an ajax file uploader.
The problem at the moment is all the images go in to a temporary folder and if more than one person is filling out the form at once that is a huge problem.

How can I assign a unique id to the page impression so I can in turn create a temp dir with the session id as its name - then once the insert statement has been made I can move the images to a new folder and delete the temporary one.