Excel interface with the real world

Hello,
I want to interface an Excel spreadsheet with the real world. For instance, in it's simplest form, I would like to enter a number in a cell in a spreadsheet and have this sent to another application running on my PC, and to read a number from this application into another cell in the spreadsheet. Eventually I would like to extend this so that I can have an external hardware device connected to the PC reading status lines (1 or 0) and a few analogue inputs, and outputting status and Analogue (i.e. A/D) signals. By running a macro in the spreadsheet, combined with ordinary formulae, I foresee the possibility to buld custom measurement and control applications in the laboratory, without the need for complex programming for each application.