Calvin Lawrence is one of my favorite IBM'ers - he's a guy who is out in the field, talking to customers about how to implement SOA. He's super-smart, but doesn't feel the need to pontificate. He communicates his expertise in a way that helps those of us who are merely chugging along without the same mental capacities to understand some lofty concepts without feeling inadequate. It's a gift. So it's for this reason that you should check out his newest piece for us: Adapting Legacy Systems for SOA:
There is no quick fix to transforming existing legacy-based systems. The journey to becoming an agile and flexible enterprise is one that must be seeded with patience. However, benefits can be realized throughout the journey, which means your company doesn't have to wait until the transformation is complete to reap the bottom-line benefits.
So, that's the gist, but you really need to read it to "get" it...there's so much more to understanding how to develop a truly services-oriented infrastructure, regardless of the baseline from which you're working...but not to worry, Calvin has made it pleasantly digestable.