For now, GRUB needs a separate ext3 boot partition when you use ext4 for the Fedora root partition. And after you shrink the Vista partition, I recommend that you leave the newly created unpartitioned space for Anaconda (the Fedora installer) to create its own partitions for Fedora. It's perfectly capable of doing that (better, really). Other than that, you have the right idea. GRUB is well-known to be able to boot Vista.