Add leading zeros to dates in Excel [aka Get rid of/convert dates with no leading zeroes (d/m/yyyy or m/d/yyyy or d/m/yy or m/d/yy)]

I have a date format that has four forms which Excel can't handle.

1/4/2009
9/13/2001
12/12/1642
11/3/2010

I need to convert them to a date. DATE() is fine. How to do it? This way:

=DATE(RIGHT(A2;4);LEFT(A2;FIND("/";A2)-1);MID(A2;FIND("/";A2)+1;IF(LEFT(RIGHT(A2;7);1)="/";1;2)))

Here's the German Excel version:

=DATUM("20"&RECHTS(A2;2);TEIL(A2;FINDEN("/";A2)+1;WENN(LINKS(RECHTS(A2;7);1)="/";1;2));LINKS(A2;FINDEN("/";A2)-1))

Here's the code for dates in the d.m.yy format:

13.11.07
3.12.07

=DATE("20"&RIGHT(A2;2);MID(A2;FIND(".";A2)+1;IF(LEFT(RIGHT(A2;7);1)=".";1;2));LEFT(A2;FIND(".";A2)-1))