If you only need to rotate around the Z axis then it is a simple 2D trig problem. The z co-ordinate is invariant as this is our rotational plane.

sub rotate {
    my ( $x,$y,$z,$angle ) = @_;
    $angle = deg2rad($angle);
    my $x_new = cos($angle)*$x - sin($angle)*$y;
    my $y_new = sin($angle)*$x + cos($angle)*$y;
  return $x_new, $y_new, $z;
}
sub deg2rad { return 3.14159265358979*$_[0]/180 };
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Here is a nice article with a pretty applet Update Corrected error noted by johnnywang

The beauty of concrete! Thanks so much for a perfect example tachyon. Also, a good page about the topic: 2D Math
jtrue

just want to point out it's not quite right. You need to first find the polar angle for the original point (x,y), then add the $angle to that for the new polar angle.

Updated. I'm only refering to the geometric meaning. There is a formula: multiplying by the rotation matrix given by ((cos, -sin),(sin, cos)) (not perl notation!)

Well, the quick-and-dirty way to do it is to scale your x component by cos(t) and your y component by sin(t). You might be happier with a matrix-based solution in the long run, though.

Edit: The math above is, of course, totally bogus. I plead momentary imbecility. johnnywang has the correct solution. D'oh!

What kind of program are you writing, btw?