i want a plain white symmetric crosshair, like crosshairimage 20, but symmetric like the one in q3
i dont know why this one is not symmetric... the lines are not the same lenght

also i need one like cg_drawcrosshair 2 in ql (a cross but with the middle opened)

if i could use the actual .png crosshairs in qw it would be great. is it legal to do this or i get kicked from some servers due unpure client?

Not sure about your skewed crosshair.

Regarding QL-like crosshair, maybe this is something:
http://gfx.quakeworld.nu/details/424/epicross/

Put in /quake/qw/crosshairs/ and enable with crosshairimage epicross2

Custom crosshairs using the crosshairimage command are perfectly fine to use.