Hi, Jerry,
What are your back-end database requirements? Would the limitations described in other posts (physical size, 1 CPU, etc.) be OK for your situation, or would you need something beyond those? Other factors, like # users, estimated database size over the next several years, etc. should also be considered.
As someone else stated, MySQL isn't necessarily "free", and doesn't yet have the full capabilities that you'll find in SQL Server.
Kevin