I only have an old disk Microsoft Office 2000 Premium but it wont install in Windows 8.1 I dont have the money to buy a new

Office 2000 is not going to be supported and probably isn't compatible with things today anyhow. You could always try LibreOffice which has pretty much the same features, will be a big improvement over Office 2000 and is compatible with current Microsoft software thanks to the EU. And most importantly is entirely free!
 
Most people can get by quite nicely with either of the 3 options presented.

They offer compatibility with MS Office and can't beat the price of free.

http://www.howtogeek.com/187663/openoffice-vs.-libreoffice-whats-the-difference-and-which-should-you-use/ and of course https://www.google.com/docs/about/ since many already have gmail, it's already included.

Good luck!
 
If you live somewhere that Office 365 is offered, it's only $70/ year, and you'll have the newest version of Office + 1TB cloud storage + a ton of skype call minutes. That is usually the best option.


As for 2000, it's possible to install it in the right conditions, since it worked on XP SP3 just fine
 


You know how many <<content removed by moderator. Be nice, please.>> say "I just bought a $2000 computer but don't have enough money for a Windows OS license" around here every week? A ton.

OP here didn't state how much money he can spend on the software or why he needs to install office productivity software now. If his "excuse" is that he spent all his money on hardware, he definitely has enough for Office 365. If is excuse is that his old machine broke and he got a used one for free/ very cheap, then things like openoffice might be good enough for now, even if they can't even get close to the performance of the Microsoft office suite