THEORY: etymology of English habitual "be"

A while back there was a discussion on this list about the present tense
habitual use of the word "be" in English dialects both in England (Penzance,
IIRC?) and America (AAVE).  I was given a set of books and tapes on learning
Irish Gaeilge yesterday and I was reminded of this thread when I read that
the Irish verb bí has both a present and "present habitual" tense, and that
the conjugation of the habitual "tense" is "bí".  Is it possible that the
existence of "be" in all persons as a present habitual in some English
dialects is a result of borrowing from Gaeilge or other Celtic languages?  is
there any corresponding form in other Germanic languages?

slán go fóill,
Seosamh Mondello