Imports System.Text.RegularExpressions
Dim data As String ="\blabla1\73\blabla2\54\blabla3\21\blabla4\blabla6\34"
Dim fragments As String() = data.Split(new Char(){"\"}, _
StringSplitOptions.RemoveEmptyEntries)
For Each fragment As String In fragments
Console.Write(string.Format("{0}:", Regex.Match(fragment,"\D{1,}", RegexOptions.Multiline)))
Console.WriteLine(Regex.Match(fragment,"\d{1,}", RegexOptions.Multiline))
Next
You could also split the source string using a regex, but that'd be overkill in this case.
The nice thing about using the regex to pick out the numeric part is that you don't have to worry about fragments that don't have an alpha prefix. Nor do you have to write lots of your own string splitting code that you then have to maintain.