yeah those calipers look like junk ... any short to medium reach dual pivot will vastly improve the braking, couple of caveats here though:

1: the frame might not work with modern calipers with recessed fixing bolts

2: if you don't know what your doing or have the tools to do the job right bring it to a shop

3. plan on spending at least 1/3 the cost you paid for the bike on the upgrade ... if you are willing to do this then I am sure the options will be plentiful

4. I'd be willing to bet that with some adjusting you might be able to get better braking out of what you have