The FileUpload.AllowMultiple
property in .NET 4.5 and higher will allow you the control to select multiple files.
<asp:FileUpload ID="fileImages" AllowMultiple="true" runat="server" />
.NET 4 and below
<asp:FileUpload ID="fileImages" Multiple="Multiple" runat="server" />
On the post-back, you can then:
Dim flImages As HttpFileCollection = Request.Files
For Each key As String In flImages.Keys
Dim flfile As HttpPostedFile = flImages(key)
flfile.SaveAs(yourpath & flfile.FileName)
Next