Here's a snap shot of a jumper from my webcam...
It looks like a piece of plastic on the outside, but on the inside, when you place it over two pins, it creates a connection between the pins... On your drive you would place the jumper over the left two pins, if you are looking directly at the
set of four pins.
If you don't have anything like this laying around, you might be able to get by wedging a piece of
tin foil in between the two jumpers. Just make sure it doesn't touch anything else.
If the foil touches any other part of the metal casing on the drive, except for the two jumper pins, you may ground out the signal. I'm sure other people have used other things..
Just remember that if this doesn't fix your problem doesn't mean you have to remove the jumper... If your motherboard doesn't support "auto_configuration" (3 Gigabits/sec) drives, then you'll have to leave it on there..
edit: Look here under "Storage Controller":
http://reviews.cnet.com/desktops/dell-dimension-4700-for/4507-3118_7-31292625.html?tag=mncolBtm;rnavYour motherboard supports only the 150 Mbps standard (1.5G)
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