I ended up moving Wubi to a new partition, and then installing Ext2 driver for Windows and Ext2FSD, in that order. (Not sure which driver is the one that did it, but oh well.)
- Shrink the Windows partition using Vista's built-in tool. (If you encounter problems, click here.)
- Create a bunch of partitions.
- Vista's tool is inadequate if you want to create more than four partitions. (Or plan on doing so in the future.)
- Reboot into Ubuntu, run GParted to create a new extended partition. Then put a bunch of logical partitions underneath that. Do not move the Windows partitions. (You may resize them, but don't move them.)
- Move Wubi to the new partition.
Automatically Mount Partitions in Ubuntu
Why does the Windows volume need to be mounted every time you boot into Ubuntu? Wanna fix it?
(If that doesn't work, try one of these: LINK 1, LINK 2.)
Mount Linux Partitions in Windows
Use Ext2 driver for Windows and/or Ext2FSD, as mentioned above. If they don't work for you, you're stuck with the alternatives on this list or this list.