I'm not a VB guy, but can do math.
' width would be the width of the display
width = 10
' position and duration of song in seconds, converted to 0-9 range
pos = position * width / duration
' don't update unless it changed
if(pos = lastpos) then return
lastpos = pos
' make a 10 char string with the ~ somewhere in the middle
Dim str
str = String(pos, " ") + "~" + String(width - pos - 1, " ")
Well, okay that's a starting point at least.