Something like:
While 1
If StringInStr ($manstr, "Dell") Then
$pcman = "Dell"
ExitLoop
EndIf
If StringInStr ($manstr, "Compaq") Then
$pcman = "Compaq"
ExitLoop
EndIf
If StringInStr ($manstr, "IBM") Then
$pcman = "IBM"
ExitLoop
EndIf
If NOT StringInStr ($manstr, "Dell") Or StringInStr ($manstr, "Compaq") Or StringInStr ($manstr, "IBM") Then Exit
Wend