What an awful problem! Just a shot in the dark
First, when you say reinstall, are you reimaging or actually reinstalling to the formatted disk. Second, this may be just a computer hygeine issue but did you defrag after reinstall (this can cause some headaches as a new install is pretty fragmented). Are the macros trying to access external data?, and if so do you have firewall/antivirus software (I've seen Norton anti-virus cause some pretty odd behavior). Also have you checked your file associations to see if vbs scripting is set to run (open windows explorer, View-->Options, click on "File types" tab and scroll down to the vbs extensions- should be set to run.
To tell you the truth, it sounds as if you are doing the same things I would do in that situation (except you haven't thrown the PC out the window yet). One last thing would be to reformat, reinstall ME, reboot, defrag, install MS office with nothing else on board, run excel and create a simple macro and see if it will run. If so then software conflicts (e.g., antivirus) may be the problem, also the macros themselves could have found a vulnerability in this machine vs the other- we have 57 Dell GX110's, and while they all have about the same FREQUENCY of problems, they do not all have the same KINDS of problems- computers are idiosyncratic.