You can key in Premiere Pro — I don’t have PP2, I’m still on PP1.5, but what follows applies to any and all keys.
Most important aspect to keying is lighting. Be sure you evenly light your greenscreen — no shadows, no soft fades from bright to slightly dimmer. Even a half-stop difference between light and dark areas of the greenscreen can make pulling a key much more difficult. Also, make sure that your greenscreen is at a similar illumination level to the foreground subject (try to keep the difference less than a stop). Do your best to keep green spill from your subject, since you don’t have the same spill supressors you’d have in AE. Use backlight on your subject, as well, to help pop the subject away from the greenscreen. If you can, even put a slightly red (maybe just a CTO) gel on the back and edge lights to help counteract the green spill.
Do use green for your greenscreen. DV (if that’s what you’re shooting) handles the green information in the frame with more detail, so you’ll get better keys off green.
If your greenscreen is well lit you can get a decent result with the Chroma Key effect. Select the color from the greenscreen, obviously enough. I find a similarity of about 15 or so works pretty well, with smoothing set to “high.” The Color Key effect is about as good, as well, and you can use the Edge Thin and Edge Feather to minimize artifacts around the edge of your subject, but it’s easy to gobble up details from the edges with thinning, so be careful.
Sometimes the Remove Matte effect is useful, too, but it can also create a jaggy edge to the key.
It’s not going to be the best key in the world, but depending on what you’re doing with it, it can be adequate.
Hope that’s helpful.
– Dex