My laptop (running Fedora 8 right now) has a LVM with 3 LUKS encrypted partitions (root, swap, home) on it. When I run the Fedora 9 Beta installer they show up as "foreign". The installer should recognize those and offer me to add them to the mount list.
We're not currently making use of preexisting LUKS partitions in this installer.
As of anaconda-11.4.0.62-1 you should get prompted for a passphrase for each of these partitions (Or are they LVs? It should work in either case.). If the passphrase you supply gives access, the devices' contents will be reflected in the partitioning screens.
The newest version of anaconda recognizes my pre-existing LV LUKS partitions and asks for a password. After that it correctly unlocks them and detects the correct file system type. But the encrypted setup is still not working out-of-the-box. See followup bug #441001