Problems with Visio 2000 std and NT 4

We've got a computer in one of our departments, running Windows NT workstation 4 and Microsoft Visio 2000 standard edition. The software, for some reason, doesn't like to boot up any more, displaying an error message. I'm unable to install the software over the top of the existing copy, because it already detects 'an up-to-date version'. I cannot seem to be able to un-install it because the un-install log is damaged. How would we be able to un-install the software? I think my last option is to delete the directory and remove all the visio keys out of the registry. If anyone can help me, could you please email me on the following address (its my work email): pkesteve@clinphone.com

Thanks,
Phil K