1. Is there any way to configure avast to use different sentivity to different folders?
I mean, can we set (maybe through avast4.ini file) special folders to be protected by HIGH sensitivity and others, common ones, with a lower protection state like NORMAL?
No, as far as I know.
2. Is there any way to generate a list of startup programs (file name and path) to be excluded from scanning? What more does avast search at logon time to scan (icons, other files, etc.)?
Well, as said multiple times, avast! doesn't scan anything
itself - it scans files that are accessed (by other applications, be they part of Windows or external), according to current settings.
Regarding the list of startup programs - well, you may edit the "Resident protection" task in Enhanced User Interface to write everything it scans (i.e. even "OK files") into the report. Then, you'll see what is being scanned during the startup (you'll probably want to turn the reporting off soon afterwards, as it will be generating a lot of additional disk activity, obviously).
However, I strongly discourage you from excluding the files - the list will be huge and the list of avast! exclusions is
not meant for such things (meaning that there is probably some size limit for the list, and more important, the exclusion mechanism itself isn't optimized for big lists, so it may actually slow down the computer noticeably, instead of speeding up the boot).
I hope I can reveal a "secret" and say that the behavior of avast! Standard Shield in Windows XP, and especially during the boot/logon, will be significantly changed in the next avast! release (to be out in a few weeks, probably). Let's hope it will be for better...
