in reply to DB Mangager
Oh, I get it, you mean DB Manager. Oh well. There's quite a few of these already, so you might consider adding to a project rather than starting your own. I usually bring up WDBI since I've used it the most, and it already works with multiple databases. It's home page is ominously silent, however; but a quick trip to FreshMeat showed me some new DB definer/managers that I'd never seen before, so no worries.
If you feel you really must write another one of these yourself, then I suggest taking most of what you have now and moving it to a module named for MySQL. Then install yourself some PostgreSQL and make another module for it. By getting at least two databases working, you'll have migrated a good portion of the non-portable code out of the main program and also will have created a framework for others to add databases, should they be inclined.