SKF: An SKF file is the waveform that is generated to present me with the graphical WAVEFORM for the Audio Tracks in my Vegas projects. When it is time, housekeeping, I delete these. I don't worry 'cos they would get recreated when I should ever reopen the Project again.
DAR: This IS the DVDA Project file. It is NOT the actual DVD and DVD structure you would want to burn, but solely the actual work you have done within DVDA. DARs are for DVDA as VEGs are for Vegas itself.
SF: Now, I know these as the project files created by the video editing packages from Vegas's smaller siblings:
VMS and, a long time ago,
VideoFactory. Why you should be anywhere near them, beats me? Have you used VMS (Vegas Movie Studio) or VF (Video Factory) lately? What's worth noting is that you CAN open these files within Vegas, work on them and save them. But then you
CANNOT reopen them again in VMS or VF!

If you DO want to work on them within VEGAS, then save them with a different name, this allows you to save the original file.
"
One would think that you would be able to save the file and then go in at a later time to mess about with Architect. Can you so this? If so, how?"
If I've understood you correctly, then yes, yes you can. And as long as I Save/Save as within the Vegas session or DVDA session I can come back to each part in 10 minutes, 10 days or 10 months!
This is my method is to - break off and save project at any point:
#1 - Finish my editing within V7
#2 - Render a completed/finished AVI. I do this to ensure I have at least a BIG ViD finished!
#3 - I then render from this finished AVI an MPG2 Video Stream only:
MyProject.mpg
#4 - I then I then render from this finished AVI an AC3 audio only:
MyProject.ac3
#5 - Open DVDA4
#6 - Locate my newly rendered mpg drag directly onto the MAIN Menu. This appears in the timeline for the video
#7 - Locate my newly rendered AC3 file and drop it UNDER the MPG timeline.
#8 - Preview to check
#9 - Go > Prepare and I take note of any warnings that need my attention and proceed to finish prepare.
#10 - Once I've finished Preparing I then burn
So, to recap: Edit and Render in Vegas > Prepare and Burn within DVDA4
Hope this helps,
Grazie