Sempron processors are available for Socket A (462) or Socket 754 today, while the Socket A versions are nothing but manicured Athlon XP Thoroughbred-B chips given the Sempron name. As a result, the Socket A Semprons run in virtually all Socket A motherboards supporting FSB333 speeds, sometimes even without updating the BIOS.
You can see how smart this move actually is by looking at typical computer markets in China or other developing economies, such as those in South America. Here, low-cost systems are clearly dominating, bringing large volume processor sales to AMD. A big role in this success is played by Socket A motherboards, whose prices are unrivaled due to the inevitable extinction of the outdated platform.
At the same time, Sempron processors for Socket 754 benefit from the assets that benefit the AMD64 processor family. First of all, there is the integrated DDR400 memory controller that works at full processor clock speed, helping to increase efficiency. SSE2 is also supported by Socket 754 Semprons, but not by Socket A versions. Finally, the prospect of upgrading a cheap 754 Sempron machine by installing an Athlon 64 at speeds up to 3700+ is attractive.
However, the future of Socket 754 is pretty clear: It will be phased out in favor of Socket 939, and also Socket M2, which is due to come early next year. As a result, the next generation Sempron will support dual channel memory. From this point of view, investing in Socket 754 won't allow you to run dual core processors in the future.