hi,
some links on help online
ELSTER
msdn.microsoft.com/.../hh934462(v=nav.71).aspx
msdn.microsoft.com/.../hh936716(v=nav.71).aspx
msdn.microsoft.com/.../hh933980(v=nav.71).aspx
Elster existing Whitepaper (NAV 2009R2\5.0)
blogs.msdn.com/.../elster-whitepaper-f-252-r-microsoft-dynamics-nav-2009-sp1-r2.aspx