I don't know if this is possible and if it is how I go about it but here
goes....

I have some data on a worksheet called Data

I have some summary info on another sheet called Summary

I want to have a message box appear when a user selects any cell in col D of
Summary where the message is the result of a lookup of the same row in Col C
against the range F1:G5000 in Data.

Hopefully this is clear but rather than pure text in the Message Box I want
the message to always be the formulaic result of
Vlookup(RC[-1],Data!F1:G5000,2,False)

How do I code that in the MsgBox () and how do I make the box appear for any
cell in Col D

Thanks a lot