compare different data-formats

Hi,

I have two data-frames which I want to match by a date-variable.

The problem now is, that the date-variable has a different format in this two data-frames.
So simply matching by this variable wouldn't work.

In the one data-frame the date-variable contains strings that look like this:

14.Aug.2012-16:32
3.Sep.2012-16:50

etc.

in the other data-frame the date-variable looks like this:

2012.08.14
2012.09.3


is there an easy way to compare these two vectors?
Or is there an easy way to transform

14.Aug.2012-16:32 
into
2012.08.14 ?


thanks!