In the 'disk cleanup' on Vista is it safe to delete 'downloaded program files?' (wouldn't that delete the
programs as well)?
In the 'disk cleanup' what is - and - is it safe to delete 'per user archived Windows error reporting'?
'per user queued Windows error reporting'?
'system archived Windows error reporting'?
'system queued Windows error reporting'?
Thank you for all of your help.

I would recommend against deleting those things.
The 'Downloaded Program Files' folder stores downloaded ActiceX controls like Adobe Flash, Sun Java, etc and it's possible you would need to reinstall them if you cleared out that folder.
Also I think the 'Windows error reporting' files are using by the 'Problems and Solutions' applet which will sometimes go out and find solutions to problems that are saved so it's helpful.

And due to some bugs with the 'Disk Cleanup' I would recommend against using it at all as it doesn't save that much space but can cause many problems if used incorrectly.

Justin is extra cautious. But he knows more than me about PCs. So why don't you go with what he says. If I needed to, I would delete that stuff. But Justin has a good point: it is probably not worth the effort - and then the Disk Cleanup program is not kosher anyhow.

Thank you all for your help - I knew I could count on you.