message class

hi i am trying to give a message that will be like this:

1234(say) g/l account is valid for the profit center 2345(say)

1235(say) gl account is valid for the cost center 2345(say)

1345(say) g/l account is invalid for the profit center 2345(say)

1345(say) g/l account is invalid for the cost center 2345(say)

i want to display any of the message depending upon the conditions.

so how can i do it???

points promised!! thanks in advance!!