rearrange columns 'in between' method

Hi folks!
i’m having an headache with this problem:
i have 2 columns (A,B) with equal lenght in rows (100000 each !!!). I want to re-arrange cells from
A1, B1
A2, B2
A3, B3
and so on…

TO
A1,
B1,
A2,
B2,
and so on…

How can i do that??

…from A1, B1 A2, B2 A3, B3 and so on…
TO A1, B1, A2, B2, and so on. (??)

This looks pretty much the same. What should actually happen?
Would you mind to post a few rows of sample data in the given arrangement and in the wanted as well?
BTW: If columns A and B contain data of different semantical classes, simply drop the idea. The “every other row” arrangement would cause trouble again and again. “PtrettyPrint” is the only exception.

hallo
Maybe something like (in C1)

=INDEX($A$1:$B$100000;ROUNDUP(ROW()/2;0);2-MOD(ROW();2))

fill down to C50000