[Question]Duplicate Names / WebBased .txt

[Question]

Ok so i am trying to make this code:
using http://ugleh.com/Tutorials/Suggestion/Suggestions.txt

Outside Link Approved by [MPGH]NextGen1

So if the program reads the file and finds two exact names, the user will not be able to post a comment. i just need help for that code.

[php]
If name is used twice:
MsgBox ("Sorry you already commented")

Else

blah....
[/php]