Sure. Install something like Paragon Hard Disk Manager (there is a free edition) in Windows and use it to shrink the Ubuntu partition and create a new one in the free space. Although Linux is pretty good at supporting NTFS the absolutely safest format to use for the shared partition would be FAT32. The big drawback with this format is that it doesn't support files bigger than 4GB (-1 byte). If you may need to store bigger files then use NTFS.
Make sure that you keep Ubuntu as the first partition on your disk (presuming it is now the first, or only, partition). As always, back up any important data on the partition before resizing.
I would download GParted and create a bootable disk to handle the resizing of your partitions. Very inutuitive and clean. Probably should backup data of course, but you shouldn't lose anything.
As far as reading your linux partition from Windows, are you using Ext4 or Ext3? If Ext3, there is a driver for Windows that will allow it to be read as usual. http://www.fs-driver.org/index.html , I'm not sure about Ext4. Linux will handle all just fine, but Windows is very picky.