I faced a similar problem a while ago and did this:

StringBuilder sb = new StringBuilder();
// Append the 40,000 entries to sb
FileNameTextBox.Text += sb.ToString();

Worked great for me!

I hope this helps.
-Jeff

   Well, I'm not sure if it well be any faster, but I'll bet this will be
more useable:
       put them in a listbox.

Hello Ty,

Are u really need all data being showed on the screen? Seems no. Just fill
that box async in the form start, thus fillin' of the box will be performed
in the background

T> I have a problem that should be relatively easy to fix but the
T> solution just seems to elude me.
T>
T> I am creating a Windows app that contains a text box that I wish to
T> fill with data from a file.  The file contains approximately 40k, 60
T> character entries and it is taking an enormous amount of time to load
T> the file contents into the text box.  Is there some way to speed this
T> up?
T>
T> I am currently reading an entry from the file and using the code:
T> FileNameTextBox.Text += sFileEntry;
T> to display the entry.
T> Thanks,
T> Ty
---
WBR,
Michael  Nemtsev :: blog: http://spaces.msn.com/laflour

"At times one remains faithful to a cause only because its opponents do not
cease to be insipid." (c) Friedrich Nietzsche