Simple question from a VB beginner

I am writing a program to take orders emailed to me as a comma separated .txt file and convert them to an ODBC database for integration into another program. The user will type an order number in a textbox, push a button and viola! it's in an Access database. I know, easy stuff right? When I'm setting up streamreader to open up the text file, I need to know how to assign a variable to the name of the .txt file I want to open. For example I have an order: C:\Orders\1001.txt I need the 1001 to be a variable (whichever order I am trying to open and is in the text box at the time) Hope you can understand what I'm trying to do here. Thanks in advance for your help! Jake