I managed to round the box I need my contents to be in with CSSPIE but I have a problem. The gradient is 100% opaque whereas I used the Microsoft gradient filter to make it semi-transparent, showing the background. I'd like to maintain that, is it possible? If I keep both, I get the faint semitrasparent outline (with square borders) and above it the opaque one with rounded corners. Help?
(I only need it to work on IE, since I have it set in a -if IE- warning and resort to border-radius and rgba for other browsers)

It's not clear from your description, is the element's background that you want to make semi-transparent a gradient or a solid color?

If a gradient, PIE is not able to do this right now (though limited support is in the unstable master code.)
If a solid color, you can simply use -pie-background with an rgba color

I had to use a gradient (which was really a solid color, the gradient's two extremes being the same) to get transparent effect since IE didn't read rbga (and Alpha filter made the contents of the box transparent, not just the graphic), but I used rgba on PIE like you suggested and now it works wonders! Thanks a bunch!