Yep.. those sandpaper and diamond discs are awsome. These are usually in the dremel section, but you combine it with a spiracut and metal is NO problem. I cut through a brass 6-7 inch diameter pipe with a 1/4 inch thickness.
I use 2 discs doubled up to cut with. Its number 426 or 420 from this page.
http://www.tri-esssciences.com/dremeltools.htm I havent used the ball shaped tools near the top. Maybe I would do better with them? Dunno. But I do know I am getting good with the discs.