[jQuery] problem in setting opacity

Hi
I am trying to set the opacity of clue tip. I tried form css and
browser.
It is working, But it is hiding the rounded corners, arrows at the up
side of the cluetip.
I am using "jQuery clueTip plugin Version 0.9.4"
I am setting opacity in css as "fiter: alpha(opacity=70)"
Please suggest me to resolve this problem.
Thanks in Advance,
Balu