How can I encrypt the conversation packets? Thanks.

George Orwell wrote:

What do you mean by "encrypt the conversation packets"? Tor is designed to
make your "packets" anonymous. To do this it encrypts them between you
and a Tor exit node. After that they're no longer encrypted unless you're
using some other IM feature or IM capable encryption software/plugin/etc.

Assuming you want anonymous IM, does MSN Messenger support SOCKS proxies?

If "yes", configure MSN Messenger for SOCKS proxy on at 127.0.0.1:9050

If "no", get a real IM client and configure it for SOCKS proxy at
127.0.0.1:9050.