I once had a working dual boot working on my computer. I had windows 7 and ubuntu running and I only had to select which system to start when starting my computer. After updating ubuntu though, the linux boot option is there but it doesn't boot anything and sits on a black screen. Windows still works fine. Any ideas as to how to fix this? Re-installing ubuntu is an option since I didn't have any permanent data on it, but I do need it now for cross platform purposes.
I would do as gyropyge suggested and try a boot-repair option first. It's possible that somehow your boot loader is not seeing the Ubuntu partition or loading it correctly.
Here is a link to the boot-repair-disk project on sourceforge: boot-repair-disk
Additionally, I would also suggest that you look into virtualization. For projects that require both Windows and Linux to be present, it is really useful to use a virtual machine. (You can emulate one from the other, but in my experience emulating Ubuntu from Windows is easier to do.)