VirtualBox running Ubuntu accessing host file system on Mac OS X

I have a few Mac OS X systems, in particular a MacBookPro that my job gave me. 2.33 GHZ w/ 2GB of memory Core2Duo. It's a fine and dandy machine and I'm real happy with the performance of VirtualBox on this system. Since my job is really about facilitating running Java on open source OS's like Ubuntu what I need is for a virtualized OS to feel very responsive. But I also need to compile OpenJDK source on that OS.