I'd use the \s+ modifier, which is easier to read
public Regex MyRegex = new Regex(
      "\\s+",
    RegexOptions.Multiline
    | RegexOptions.CultureInvariant
    | RegexOptions.Compiled
    );
// This is the replacement string
public string MyRegexReplace =   " ";
string result = MyRegex.Replace(InputText,MyRegexReplace);
Or in VB
Public Dim MyRegex As Regex = New Regex( _
      "\s+", _
    RegexOptions.Multiline _
    Or RegexOptions.CultureInvariant _
    Or RegexOptions.Compiled _
    )
Public Dim MyRegexReplace As String =  " "
Dim result As String = MyRegex.Replace(InputText,MyRegexReplace)