Every nth day of the month

I need to programmatically determine the date of the nth day of the month or the xth day of the month if it's already past.

For example, what is the date of the 3rd Tuesday of this month?  If it's already past, then what is the date of the 3rd tuesday of the next month?

To go along with that, what is the LAST Thursday of the month? (for example).

To be clear, I don't SPECIFICALLY need Tuesdays - I need this to be flexible for any nth day (any day) of the month

I can think of a couple of possible ways of doing it, but they involve LOTS of repetitive code...  

Thanks in advance!

(I need this specifically for ASP classic, but I figure that Access and Visual Basic, being so similar, will work as well).