So the gf and i were having a really intense sex session. She was riding me and she said that she had an early xmas gift for me, at that point she pulled out a small vibrator. now i've never used one, and she didn't either, so although it made her wet, i really am not sure how to use one to get a girl to orgasm. any guys have some tips for a guy using a vib on his gal?

If it is a small vibe use it gently at first on her clit. The best way to get it figured out is let her masterbate with it when she has time to figure out what feels good to her. I recently bought a stronger one and I will put my cock on her clit with the vibe on top of my cock. Mutual pleasure.

I got my wife a Pocket Rocket (because we saw Courtney Cox using one in a short lived cable series she did called "Dirt" Sexy as all hell, it made my wife so horny she asked me to get one for her.)

Anyways, I'll be dammed if I can get her to cum with it. I spent hours trying and begging her to instruct / direct me how to use it to make her cum. It's only when she uses it her self that she climaxes. Of course it helps tremendously that I suck on her nipple and wiggle my thumb in her pussy while my index finger taps her rose bud. When she cums, I can feel her pussy contracting and spasaming on my thumb. It's AWESOME!

Oh, and here is the vie clip of Courtney getting off:
Courtney using a Pocket Rocket

Some of the gals I worked with raved about something called the "Eager Beaver". It's a y-shaped device for multiple stimulation points.

Google it ;-)

What I do with my gf is like said above. Play with her clit and get the vibrator to make her hot and horny. If it is the size that would work well put it up against her g-spot and push the vibrator against it. If you know where her g-spot is it will send her over the edge.