Is there a way to get IE7 to correctly calculate the width of the block inside absolutely positioned container?

If you just need to specify the width of the inner element in percents from the parent, you can come up with a solution.For example, you specify 50% width:
\r
\r

i i i\r

Why not do so instead of specifying width:
\r

.child { left:0; right:0; } 

\r
There are of course limitations (will only work in IE7+), but in this case it is better than expression.