P2P programs supported include Kazaa, KazaaLite, DirectConnect, DirectConnect++, WinMX, LimeWire, BearShare and BitTorrent (some of these are only supported under Windows NT/2000/XP/2003).
I don't belive there is any plans to support soulseek, but i may be wrong, im sure somewone will correct me if i am.
EDIT: It may be included in the Avast! V4.5 that will hopefully be out soon.
--lee