It took me so long to find this out. So long being 3 hours.I'm slightly protective over what seems to be a VB secret but here you go :lol:
Line (x1,y1)-(x2,y2), RGB(X,why,Z), B
That 'B' after the colour parameter makes the line turn into a rectangle somehow; no idea how or why but it does.
Also just in case, make sure you don't add any drawing functions on the onLoad() event 'cos they won't work.
[EDIT]: Curse these filters! :D