URL Encoding using C#

I have an application which sends a POST request to the VB forum software and logs someone in (without setting cookies or anything).

Once the user is logged in I create a variable that creates a path on their local machine.

c:\tempfolder\date\username

The problem is that some usernames are throwing "Illegal chars" exception. For example if my username was mas|fenix it would throw an exception..

Path.Combine( _      
  Environment.GetFolderPath(System.Environment.SpecialFolder.CommonApplicationData), _
  DateTime.Now.ToString("ddMMyyhhmm") + "-" + form1.username)

I don't want to remove it from the string, but a folder with their username is created through FTP on a server. And this leads to my second question. If I am creating a folder on the server can I leave the "illegal chars" in? I only ask this because the server is Linux based, and I am not sure if Linux accepts it or not.

EDIT: It seems that URL encode is NOT what I want.. Here's what I want to do:

old username = mas|fenix
new username = mas%xxfenix

Where %xx is the ASCII value or any other value that would easily identify the character.

Solution

Edit: Note that this answer is now out of date. See Siarhei Kuchuk's answer below for a better fix

UrlEncoding will do what you are suggesting here. With C#, you simply use HttpUtility, as mentioned.

You can also Regex the illegal characters and then replace, but this gets far more complex, as you will have to have some form of state machine (switch ... case, for example) to replace with the correct characters. Since UrlEncode does this up front, it is rather easy.

As for Linux versus windows, there are some characters that are acceptable in Linux that are not in Windows, but I would not worry about that, as the folder name can be returned by decoding the Url string, using UrlDecode, so you can round trip the changes.