Does anyone know whether one can install DOS on a computer that has been set up to run the latest Win OS without corrupting it?
Yes. You must re-partition your hard drive to allow for booting into DOS. Partition Magic is a software package that will allow you to do this. You can boot into any operating system you have individually installed on relevant partitions. But, you can't switch from one OS to the other without rebooting.
Looks to me like it might be less painful over the long run to go ahead and bite the bullet and adapt to an updated spreadsheet program. But that's JMHO.