IBM has released a free version of DB2 named DB2 express-C. It is free for development, deployment, and redistribution. It is supported on the x86 and x86-64 architectetures and is runs on Linux and Windows (2000, 2003, XP). Added to that, this version is seamlessly upgradable to DB2 UDB, if the requirements change. The catch here is: DB2 Express-C is designed to only run on systems with a maximum of two processor cores, or dual-core processors and upto 4GB memory.
It is available for download on IBM downloads.
There is also a DB2 express forum, where you can get community support for this product.