Saving A Modified TextBox Entry

Okay, that snippet made the file I was trying to open in the %USERNAME%AppDataLocal folder worked perfectly, again, many thanks - But now I'm 3/4 of the way through my program, and I've hit a wall - I have the exact same program I made in VB6, and it works to perfection, but I am TRYING to switch over to .NET, and am finding a lot of difficulties in getting certain things to work - My biggest headache right now [ Which is basically the finishing of my program ] is a bit hard to explain, so this may be a rather long post: One of my programs that I use to keep track of my Music hard drive outputs to an XML file, in which there is one line I would like to be able to 'Replace' through the program I am making now to a different user-defined string, and close [ Applying string change/save ] the XML file. I have my Main Form, a TextBox1 [ I can't get the XML to open in a ListBox like I wanted ], TextBox2, a 'Locate String' Button, a 'Modify' Button, and an Exit Button. I open the XML file with this in my Form1_Load event into my TextBox1:[code]

The <DateValue> is the line I want to be able to modify [ Which the entire string looks like this: <DateValue>2010-04-10T10:00:03.5009756-04:00 </DateValue>, and I want to be able to change the date and time to whatever the user specifies ], which once the XML is loaded into TextBox1, when the 'Modify' Button is clicked, that string is then loaded into TextBox2... This is where I am lost - How can I apply the modified string to the TextBox1.Text [ Entire XML file ], and save it upon program end, without the rest of the XML lines being disturbed? I realized I needed another Button - The 'Modify' Button now loads the selected string into TextBox2, and I have a 3rd Button to 'Apply Modification', which I want to update the <DateValue> string in the TextBox1 [ Full XML file ] from the modified string in TextBox2, then save on exit - Hope this helped clarify things.So here's the routine:

1. Form loads, opening the XML file, and loading it into TextBox1.
2. User clicks 'Modify' Button to load searched string into TextBox2.
3. User modifies TextBox2 entry.
4. User clicks 'Apply Modification' Button, which changes the searched string in TextBox1 to the modified user-defined string.
5. User clicks 'Exit', which saves the XML changes from TextBox1 [ Without messing up the XML file format ], and the program ends.