If you've got the account set up only in telepathy, then you can initiate a chat by opening Messaging, tapping the speech bubble icon in the bottom right corner, then selecting a contact from the list.
I've attached provider and service files for gadu-gadu. Copy them into /usr/share/accounts/(providers or services), delete your old mc-tool account and register a new one with the Accounts app. There are no gadu-gadu icons in harmattan - you'll have to make some Let me know if it works, I don't have a gadu-gadu account to test with.
dddc143e2432ea47dfcd37a1b6a79c27 libpurple0_2.10.0_armel.deb cdf2125d37ab0880f05f2979c17d1895 telepathy-haze_0.5.0-1_armel.deb d49d6187fda29ea5d051a5479201e0d0 im-providers-additional-0.2.deb eff0337a3af7459bb9a10b7ca1ed6c62 im-providers-additional-0.4.deb