Bezier curves - mirror and extrude

Support Basics & Interface
1

I want to draw this using bezier curves:
http://i65.tinypic.com/ab4klx.jpg
And later extrude it.

In Edit mode I have this:
http://i65.tinypic.com/1zy8nww.jpg
I´ve drawn only a quarter and then I´ve used the mirror modifier on X and Y axis.

The problem is that I can´t extrude it properly. I´ve tried converting the curve to mesh but the result is this:
http://i68.tinypic.com/24eauxg.jpg
Making this I can extrude, but I can´t use the boolean modifier to make the two holes (view first image).

How can I do it?

Thanks and sorry for my english :smiley:

2

Add the holes with additional curve circles and set the the curve to be a 2 curve

but I can´t use the boolean modifier to make the two holes (view first image).
Why not ?