If it's a SATA drive, it's compatible with new builds. If it's an old IDE/PATA drive, the new motherboard would require and IDE connection port or you could possibly use an IDE to SATA data cable. No real risks involved.
As your hard drive gets older the chance of failure increases exponentially. This is why most warranties only last 1-2 years. Just be sure to have a good backup solution in place - which should be standard practice anyway.