Examples and tutorials about popen2/3, smtplib/multipart and icq/jabber?

Is there any good tutorial/example about popen2 and popen3? I have to
execute a given command on Linux and Windows from within a Python program.
If possible, on Linux I would like to be able to set the executing user
(setuid) and the niceness level of the command. (and yes: I know it is a
dangerous feature...)

Is there any good tutorial/example about smtplib and MIME multipart
messages? I need to send a bunch of e-mail messages (possibly in HTML
format) to many diverse recipients, each message with one or more
attachements (typically PDF files).

BTW: how about using Twisted Matrix for this task? I heard it is able to
send e-mail messages asynchronously (leaving free the invoking program to
go on just after the call to the "send_msg" function).

Is there any good tutorial/example about Jabber or ICQ and Python? I have to
send a bunch of instant messages (possibly with one or more file and/or one
or more URL attached to them in some way) to many diverse recipients (I
normally do not use ICQ and/or Jabber and I know them very little. Any
advise or suggestion about this task is greatly welcome).

Thanks in advance

-----------------------------------
Alessandro Bottoni
.