[MacDV] Render files - Delete

[KS]

Sorry, this message came back so I'm re-sending.

I'm a new FCE user with about 4 months experience and 4 long form  
videos. I'm wondering if I can delete all the extra Render files I  
find scattered in different locations on my external drives.   Once I  
complete a specific project  if I trash the render files related to  
that project  will I be able to revise/update the video at a later  
date?  How is that done?  Should I export to MiniDV tape and re- 
import it when I want to update?

Sometimes when I try to open a new project I keep getting the last  
thing I worked on opened up – why can't I get a brand new project to  
start with?

I don't see that issue addressed in Tom Wolsky's book  although  
maybe I've missed something.

Thanks for any help.

ks