Silvercord: Rotate around an arbitrary axis

I addressed this to SC but anybody who can help is welcome since I'm frickin' lost. What I want to do seems fairly simple but I just can't seem to get it right.

I have a vector that I want to rotate about (0, 0, 0); kind of like a clock hand rotating. Here's what I tried:

original vector: (0, 1, 0)

angle to rotate 90

rotating around z axis at (0, 0, 0)

rotated vector.x = cos(90) * original.x + sin(90) * original.y

rotated vector.y = cos(90) * original.y - sin(90) * original.x

I'm sure that I'm just doing something wrong in my algorithm or missing a step somewhere.

Thanks in advance for your help.

Jason