I have been living in Lithuania since 1991. Therefore you will find more documentation about this country's borders than any other!   But I am far from finished...

Do also look up under «Byelorussia» - there you may find the Byelorussian-Lithuanian-Latvian tripoint and the Adutiskis border city.

You will also find more about Lithuania under «Places of Interest»

Literature:

In English (From the Lithuania's parliaments files):

REPUBLIC OF LITHUANIA: LAW ON THE STATE BORDER  AND PROTECTION THEREOF (May  9, 2000. No. VIII - 1666)

Lithuanian only (From the Lithuania's parliaments files):

Lietuvos Respublikos ir Rusijos Federacijos sutartis "Dėl Lietuvos ir Rusijos valstybės sienos" 
[Republic of Lithuania and Russian Federation Treaty "About Lithuania's and Russia's State Border) 
(Ratificated 19 Oct 1999 - valid after Russian ratification)

Lietuvos Respublikos ir Lenkijos Respublikos sutartis "Dėl bendros valstybės sienos, su ja susijusių teisinių santykių, taip pat dėl bendradarbiavimo ir abipusės pagalbos šioje srityje"
[Republic of Lithuania's and Republic of Poland's Treaty "About Common State Border, and its Legal Situation, also About Co-operation and Common Assistance in this Fied] 
(Ratificated 2 Jul 1996, valid 23 Dec 1998)

Lietuvos Respublikos ir Baltarusijos Respublikos sutartis "Dėl Lietuvos ir Baltarusijos valstybės sienos"
[Republic of Lithuania's and Republic of Byelorussia's Treaty "About Lithuania's and Byelorussia's Border"
(Ratificated 23 Apr 1996, valid 26 Apr 1996)

Lietuvos Respublikos ir Latvijos Respublikos sutartis "Dėl valstybės sienos atstatymo"
[Republic of Lithuania's and Republic of Latvia's Treaty "About the State Border's Establishing"]
(Ratificated 26 Jan 1995, valid 5 Jul 1995)

Maps of Lithuania 
http://litauen-nytt.tinklalapis.lt/KART.HTM