can WP incorporate content from other database or be a wrapper for other content

Hello, I have a strange question to ask.
I run a website with some custom php code and a custom MySQL database. I would like to migrate the entire site to WP but i can’t afford to loose all the content that currently makes up the site, so I was wondering if there is some way to incorporate the website’s content into WP blog entries some way…
I have used Mambo once and I remember it had a way of “wrapping” extraneous content within a Mambo page, if you know what I mean.