>> Can I select a default path for the upload control in ASP.NET
Probably not, as this is a client's browser setting. You *could* do it with VB
Script (by setting a registry key) at the client but this requires insane low security settings and as such will work in a very controlled environment only.
>> And is there any way to upload .bak(backup) file by fileupload??
Yes. You can upload any file you want with the asp:FileUpload control; it's doesn't restrict you in the files you can upload.