simple UPDATE statement...

Hello,

I have a quick questions... consider the following information:

I have a table 'customers' which looks like the following:

firstname | middlename
-------------------|--------------------------
Johnathan C
Mark S
Joshua
Susan T
Jennifer
Marcus D
Mike G
Ted
William R

I would like to write a SQL update statement that yields the following
results:

firstname | middlename
-------------------|--------------------------
Johnathan C
Mark S
Joshua
Susan T
Jennifer
Marcus D
Mike G
Ted
William R

Basically, this... I need to take the middle initial from the
'firstname' field and place it in the 'middlename' field - that is if
only there is a middle initial in the 'firstname' field.

Please let me know the best way to write the UPDATE statement. If you
have any questions or need more info from me please feel free to email.

Thanks!!!