It's so old a DOS program it just might work. Just copy the folder with the program in it, then go into the command prompt, cd into that folder, run the program and see what happens. Support for printing might be a problem, but you probably can import the spreadsheet into OpenOffice Calc or Microsoft Excel and use File>Print there.
You might need to make a .pif file (if such still exists in Vista).
I'm sure I have a old backup cd or DVD with Lotus-123 somewhere (carried over from DOS to Windows 95, just in case I would need it) and I could see what happens if I insert that on my sons Vista laptop, but somehow I'm not that interested to do it myself. But if you go to a shop with such a CD and tell them you want to buy a certain machine, provided it can run the program, they surely will be willing to try it. Maybe even one of your friends or family does have a Vista PC?
Please tell the result of that experiment.
Of course, you can still buy a PC with Windows XP if you prefer.
Kees