operator hardware input

I'm replacing some old equipment and I
need a way to communicate a simple switch
closure to a VB program. What are some ways
to do this? Serial port? It needs to be low
overhead and as simple from a hardware
viewpoint as possible. The existing program
otherwise is 80 pages plus so variable
allocations could be close to limits already.

I was modifying keyboards by wiring the switch
across the enter input but newer keyboards are
hard to work with.

Thanks.

Here is an idea that I haven't tried but might work. If you use a
mscomm control, and wire the com port transmit line through the
switch and back into the receive. Every so often, you send a
character and look for that character to be returned. If it isn't, the
switch is open. Like I said, just a wild idea that occurred to me.

Another alternative would be to use the joystick port. It would allow 4 input switchs. You need to use the joyGetPosEx function to read the buttons.
Type JOYINFOEX
dwSize As Long ' size of structure
dwFlags As Long ' flags to indicate what to return
dwXpos As Long ' x position
dwYpos As Long ' y position
dwZpos As Long ' z position
dwRpos As Long ' rudder/4th axis position
dwUpos As Long ' 5th axis position
dwVpos As Long ' 6th axis position
dwButtons As Long ' button states
dwButtonNumber As Long ' current button number pressed
dwPOV As Long ' point of view state
dwReserved1 As Long ' reserved for communication between winmm driver
dwReserved2 As Long ' reserved for future expansion
End Type

Declare Function joyGetPosEx Lib "winmm.dll" (ByVal uJoyID As Long, pji As JOYINFOEX) As Long
You can look at the details in MSDN.

Thanks for the ideas. I just need to pick
my poison now. :-)