Create Acronym (Extract first letter of each word)

How can I extract first letter of each word in Excel XP?

For example:
I am a boy
You are a girl

Using the pseudo-function called acronym(), the result will become:
IAAB
YAAG

I'm using Excel XP.
Is there any function which can do it?
If not, could anyone provide a macro for me?
(I'm only a beginner in macro)

Thanks.