I learned on bamboo over 2 years ago. They were nice for a beginner because the stitches don't slip off as easily. You can rub them between wax paper to make them slicker if you knit really tight. Once your gain more control over the yarn and your tension, metals become quite fast. I even enjoy the metal "clicking" and it even makes for a rhythm that is rather relaxing.
I would do a small project first on short straight needles(Bubbles, the fish dishcloth on knitalittlemore.blogspot.com is really easy, fast and cute--also one with fins), and then try something on circulars with a short cable, so you can get used to the difference. They are nice to get used to when you are ready for larger projects or working in the round. Happy knit'n!