I think this will be possible using the 12.10 installation disc.
during the installation process you will be prompted with a question with a few options to chose from. some of them are "ubuntu alongside Windows 7", one is "replace all". Chose the advanced option. here you will see your partitions.
Windows 7 will have (at least) 2 partitions, one of which has around 100 MB and one of size you specified when you installed windows 7 (or at some point after). It is important that you leave both of these untouched.
chose to remove partitions that belong to your Fedora install. This will remove any files stored under one those partitions, but Windows 7 will be left untouched.
then make a partiton for "/", and 1 for swap should you need hibernate or if you have a low amount of RAM.
when Ubuntu 12.10 is installed and you have rebooted you will get a grub 2 greeting screen, here you can chose from Ubuntu or Windows 7. This will come every time you reboot.