Lithuania is part of the Schengen Area so you won’t need a visa for Lithuania but for the whole Schengen Area. Border controls will be at the point you enter the Schengen Area (which includes a lot of European countries) but not necessarily in Lithuania.
In general people living in countries of the EU or the Schengen area and people living in countries having visa facilitation agreements with the Schengen area don’t need to apply for a visa. If you are not sure, here is a list with list of countries, whose citizens do not require visas to enter the republic of Lithuania.
All other countries will need to apply for a short stay visa (Schengen visa) with whom they can stay up to 90 days in Lithuania. More consular information can be found in website of Ministry of Foreign Affair of the Republic of Lithuania.
Please contact IWPMA 2015 organizers in you need visa to come to the conference.