Good Mornin' AzureWolf...
You will be/have been asked to challenge for the position of ArchDruid of the Grove. If you win the challenge, then you will be elevated to ArchDruid. I don't believe that this correlates to the rank of ArchDruid (as you are thinking of it) in AD&D. You won't get any additional powers from becoming ArchDruid IIRC...you simply complete the stronghold quest and gain a place to rest. There has been some discussion that Druid powers will be increasing in ToB and will perhaps come more in line with what AD&D outlines.
Hope that helps!
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Now where did I leave that doughnut?!