First, don't do anything that would write to the disk until you make a plan.
If the data is very important, then consider cloning the disk before proceeeding. Otherwise, you need to run from a live CD or install the disk in another computer.
Things to try:
Boot from the Windows CD, go to recovery mode and enter "fixmbr" (At least this is the traditional Windows drill---Win 7 will have something equivalent.)
Boot from a Linux "live CD" (Your Ubuntu disk is probably one), open a terminal and run "fdisk -l". ("sudo fdisk -l" on Ubuntu)
The standard data recovery tools are photorec and testdisk. http://www.cgsecurity.org/
These may be available on some live CDs (eg Knoppix)