replace all # chars in a text where the first with and second in through the text

[Steven De Ketelaere]

Dear All,
 
I'm a newbie concerning Perl and need to solve a simple?? issue, I want to 
replace all first # characters with <b> and second # characters with </b>
 
Example : This is a #text# in which I would like to #replace# all # characters.
Would be : This is a <b>text</b> in which I would like to <b>replace</b> all # 
characters.
 
Note!
If only 1 # character is found I do not need to replace this, as in the end of 
the example.
 
Thanks for providing a solution ;)
 
Kind Regards,
Steven