I am trying to adjust some of the background themes from ARCH, but the graphic editor in the program leaves a lot to be desired. I want to bring it into PS, but they are .thm extension and won't open there. Any ideas?

The following paths are for XP Pro.
Not sure about Vista.

DVDA 4.0:
C:\Documents and Settings\UserNamer\Application Data\Sony\DVD Architect\4.0\Themes

DVDA 4.5:
C:\Documents and Settings\UserNamer\Application Data\Sony\DVD Architect Pro\4.5\Themes

DVDA 5.0:
C:\Documents and Settings\UserNamer\Application Data\Sony\DVD Architect Pro\5.0\Themes

Open up any of the folders and you'll have access to all the images used in a particular theme.

If you first create exactly the background you want in your Paint program, this can be imported into DVDA then saved as a Theme for future use.