I have made a page that allows users to upload files to the server using a FileUpload Control and handling its event with this code
Sub SaveAttachment()
Make sure to end your Response by calling Response.End() after Response.WriteFile(filepath) or else your form will be appended to the stream and sent to the client.
It will affect other files as well though most likely only be seen as garbage at the end of the file and ignored by their respective applications.