The only way to truly reduce noise for long exposures and high ISO for digital cameras is to invest in a camera with larger CCD/CMOS sensors. At this point in time, this means D-SLRs.
Other than that, noise is an inescapable limitation that we just have to live with. Some cameras have built-in "noise reduction" algorithms to minimise the effect of hot pixels for long exposures, and this can be replicated manually (albeit with a lot more work) using Photoshop etc. However, this is only a workaround and doesn't really solve the fundamental problem.
IMHO, digital cameras (at least at the prosumer level) are simply not ready for low-light photography at this stage in their development. If you're going to do a lot of low-light photography, stick with film for this purpose.