Hello and Welcome to the board Blubba.

Not sure about that UDF as I've not used it myself and a bit too lazy to go look up it's usage, but here is a simple method that should work.

Code:
Select
  Case InStr(Join(Split(@IPAddress0,' '),''),'10.18.132')
    'Your IP is within the range 10.18.132 so we will install a printer ' ?
  Case InStr(Join(Split(@IPAddress0,' '),''),'10.10.34')
    'Your IP is within the range 10.10.34 so we will install a printer ' ?
  Case 1
    'Not within any correct IP Range so no printer installed. ' ?
EndSelect

 

Notice that we are removing the padding (spaces in the IP) from the lookup.