Darren,
Here is another alternative for you: McObject's eXtremeDB, the first embedded in-memory database for embedded systems, released in September 2001.
eXtremeDB is written in C, and you can license the source code for a reasonable amount of money. Compile in/out the features you need. eXtremeDB delivers everything you expect a database to deliver: transactions, indexes, high level data definition language, and so on.
You can download a free, unlimited time evaluation copy from our website, plus all the documentation, white papers, etc.
Regards,
Steve
http://www.mcobject.com