Hi there,
I'm having this same problem. I bought a new laptop and installed Vegas Movie Studio Platinum and DVD Architect 3.0. It's definitely not an issue of not having enough space on my computer because it's brand new and the video file is only 45 seconds long.
One of my co-workers fixed the problem by creating a new folder in my C: drive. That solved the preparing problem, but when I tried to burn the project, it said I wasn't logged on an an administrator and thus wouldn't burn. I've posted a topic on this hoping to get an answer. I never had a problem like this using these programs on my desktop with XP, just my new laptop that has Windows Vista. I'm kind of wondering if Vista with its security measures is the issue.
Since you posted your topic a couple of weeks ago, I hope you were able to solve your problem!

Have either of you seen this thread?

http://www.sonycreativesoftware.com/forums/ShowMessage.asp?MessageID=574634&Replies=2

if it helps, *Might* also try altering the settings for default folders. Also be aware that the same program can install differently in Vista depending on if the UA BS is on or off [I believe more virtualization if UA on]. If you need to repeatedly run an app as admin for example you can specify that in a shortcut on the desktop or start menu.

Thank you so much I missed that thread!
It worked!
now I just have to figure out why its burning to ISO Device?

If DVDA doesn't list any devices other than ISO Image Writer, it usually means it can not detect a valid DVD burner. What brand and model is your DVD burner, and how is it connected?

Rob