ASP.NET FileUpload check if file exists in SP

Hi,

I have WebPart and it has a ASP.NET FileUpload control to upload files to a SP document library.  I also have method which will check if a file also ready exists in the document library and gives the user to overwrite the file.  But once a postback happen to check if file exists the file info is lost in the FileUpload control.

Can some one help me with this.  

Thanks.

Regards, Vikram