Hi Vlk. Sorry for the gap in communications, had a busy couple of days and no time to mess with this stuff.
Ok, the new version (4.7.827) is functioning fine on my machine (to recap, Win2k SP4), but the permissions are still not all correct. Some files, such as ashAvast.exe are still showing Everyone - Full control. This is definitely an improvement over having no permissions set at all (as the program won't run at all in that situation), but still not as secure as it should be (although I had never inspected the permissions set by previous versions until the problems arose with 4.7. After reverting to 4.6 a couple days ago and going to check, it was installing as Everyone-Full Control as well.)
And an fyi, I don't think that I meet any of the 3 criteria you mentioned. Not running NT4, I install to the default directory (and with the 'typical' setup), and I am pretty sure that I formatted this drive to NTFS before installing Win2k on it.
I also don't have the other thing you mention. My Program Files folder is set to Administrators and SYSTEM with Full Control, as is the Alwil folder (with vers 4.7.827), and the avast4 folder under that. The only place that permission settings seem to be the least bit wacky is inside the avast4 folder.
Last night I hed tried installing 4.7.826, which wouldn't run at all (again), so I uninstalled it and installed the latest version of AVG, just to see what would happen. AVG installed fine, with a rather detailed set of permissions on all of its components. I ran a full test just to reassure myself (with different software) that I did not have something nasty interfering with stuff. Came up clean (as I do with the current install of Avast).
Most curious, but I am glad that Avast is at least running again now.