command.com is the same command.com as it always used to be - since the old DOS until Windows ME. I don’t know what the “normal command” should be, but I think there is only one command.com in the system. (The fact that it’s EXE file, actually, is another thing; but it was always called .com).

The JetNNN.tmp files are temporary files of Microsoft Jet drivers (utilized by avast! as well). There are usually 2 files in the TEMP folder locked (in used when avast! is running), the rest of them should be possible to delete.
Btw, if there are more and more JetNNN.tmp files in your TEMP folder, you may try to update to the latest MDAC (downloadable from Microsoft) - it may help.