bezier curve

i use this code:

p[0][0]:=-0.7; p[0][1]:=-0.7;
p[1][0]:=-0.7; p[1][1]:=0.7;
p[2][0]:=0.1; p[2][1]:=-0.7;
p[3][0]:=0.7; p[3][1]:=0.7;
glLoadIdentity();
glMap1f(GL_MAP1_VERTEX_3, 0,1, 3,4,@p);
glLineWidth(2.0);
glBegin(GL_LINE_STRIP);
for i:=0 to 30 do glEvalCoord1f(i/30.0);
glEnd();

it’s very simple, but when i increase glLineWidth parameter, then it will draw wrong. there are some error in continuity of curve.
how can i do the drawing correct?
thanx

eL
eL@email.cz http://el.zde.cz