3d plot of a curve



The manual tells how to get a plot of a surface in 3 space (torus,  
klein bottle, moebius band), but how do I get a plot of a curve?   
Preferably parametrized by t:

x[1]:.5; x[2]:sqrt(1-x[1]^2) * cos(2*t); x[3]:sqrt(1-x[1]^2) * sin(2*t);
plot3d([parametric, x[1],x[2],x[3], [t,0,2*%pi]]);
gives:

Bad Range
FALSE must be of the form [variable,min,max]
-- an error.  Quitting.  To debug this try DEBUGMODE(TRUE);)

thanks