First, get the current date, then prefix it in a formatted manner:
Dim now As DateTime = DateTime.Now
txtReqDocPath.Text = now.ToString("yyyyMMddhhmmss_") + ofdDocToUpload.FileName
You may have to change the format string, I can't see how you get "2011310155114" from yesterdays date!
There is a full list of the format specifiers here:
Formatting a DateTime for display - format string description[
^]