if you want to know how to test rotated rect for collisions search for hyperplane separation theorem... i give you the example you need...
if you want to rotate use rotation matrix... :)
as i see you work in 2d so its easier...
1)for each rectangle(lets call this own_rect)
2)for each line in the ownRect
3)check the points of the other rectangle(lets call this other_rect)
4)if all the points of the other_rect are on the same side of the line AND
all the points of the own_rect are on the other side of(or on) the line
->there is no collision
5)else continue (there may be a collision but we are not sure yet)
Not finding a line that "separates" the rectangles means you have a collision :)
it is very easy to use this algorithm in 3 dimensions... but instead of lines you have planes...
I hope i helped..!!! :)