You should use an IF...ELSE... statement if you want to evaluate a condition.

With your query you're assigning the value to the variable, not comparing. It should be like this.

IF @CurrentDay = DAY(CURRENT_TIMESTAMP)

PRINT 'Today is the 24th day of the month'

After that, you should use the ELSE and generate an error. I will leave this to investigate and come back and ask for specific questions.

Here's a guide:

http://msdn.microsoft.com/en-us/library/ms178592.aspx