Uploading Large files in backgroud in a time interval

Hi all,

What is better way to large upload file.

using a web service or in application itself.

If in application, how can we check that files is to upload in a regular interval.

actually i dont want user to wait for complete uploading, when it starts uploading user will get response of uploaded and uploading will be done  in backgroud.

I am not sure this type of task can be done in webservice also so that user doesnot need to wait for complete uploading.

and one more query which event fires when the page redirects to another page.

Is it Page_UnLoad or Dispose

Any suggestions is appreciated.