[Xy-pic] Rotated frames

[Mono]

Hallo,

am pretty new to xy-pic. It looks to me very pretty though when it 
comes to labeling pictures that are loaded via xyimport.
i usually put some framed text somewhere and draw some arrows like 
that:

\begin{figure}
\begin{xy}%
\xyimport(1,1){\includegraphics{picture}};%
(0.500,0.300)*+[F**:white:<3pt>]{\txt{some text}}="a";%
(0.375,0.400)*{}="b";%
{\ar "a";"b"};%
\end{xy}}%
\caption{some caption}
\label{f:label}
\end{figure}

now i want the text and the frame rotated. i tried

(0.500,0.300)*+[F**:white:<3pt>][@!90]{\txt{some text}};%

but that only rotates the text. the frame remains non-rotated.

could you please give me some hint on how to rotate the frame as well?

btw, i use pdflatex to create the final pdf document.

thank you

Mono