Garmin to Ipaq cable wiring ?

I purchased an Ipaq to USB cable, with the intention
of making a simple Garmin GPS to Ipaq cable by cutting
off the USB plug and wiring a 4 pin Garmin plug there
(it's a Garmin 12). Thats fine, I see 4 cables which
the Wikipedia USB pages ( http://en.wikipedia.org/wiki/Universal_s
erial_bus ) tells me a
Red (V+), Black (Gnd), White (D-), Green, D+). But
these pages explain USB uses duplex communication and
it's not clear to me which Data cable to connect to
the Garmin Tx/Rx pins. IE: D+ to Rx, or D+ to Tx?
Anybody already made one of these and can enlighten
me? I have a multimeter but the Ipaq end plug is TINY
and I don't believe I could tell if my multimeter probe
was on pin 7 (RXD, to Garmin T) or pin 8 (TXD, to GPS
R) (Ref. http://pinouts.ru/PDA/ipaq_22p_pinout.shtml
).