am trying to write an vb.net app that will read a text file, look for specific lines and when they are found....replace that line with something else leaving the rest of the file the same. The file order must stay in tact, that is I can not just append to the end or beginning. The change needs to be made exactly where the line occurs in the text file. Can anyone help me as to how this would be done?

I assumed that vb.net is Microsoft Visual Basic .Net right?

Therefore it is not a linux issue.

But as I remember (I have give up windows for half a years), you will have to use stream to do so.
Go to MSDN website or get the MSDN CD and search for the details about how to use stream.

I have written a program on VB.Net which can operate with text file.
It didn't solve your problem directly, but you can use it for an example (or use it instead of notepad) about how to use stream.
That is not a good soft but I hope it have something helpful for you.
Download it at http://super-write.sourceforge.net

De Ja Vu anyone..

Forgive me for my poor English, but can you express your idea in a easier to understand way?