Final fantasies 7&8 were released for computers too.
Ok this is a bit more complicated if you never heard the word "emulating".
A console can be emulated. That means, that a more powerfull console (usually computers) can run other consoles' games on them. This can only happen through programs called emulations.
To use an emulation you need a rom/ISO to run on it. As you mentioned on your post, you want to play the ps1 games. You need to get the playstation 1 emulation called ePSXe. Download ePSXe 1.5.2 (DO NOT download 1.6. It freezes the final fantasy games). After you download the ps1 emulation, you need to find some plugins (if the emulation does not have some with it) and the ps1 BIOS. The plugins emulate different parts of the ps1 system so they can work on the computer. The graphic plugin is for graphics, other is for emulating music, other for making the keybord work as the controller etc.
The bios files is absolutly necessary or the emulation wont run your games.
You put plugins into the plugins folder in the epsxe folder and bios in the bios folder in epsxe folder.
Then you need an ISO or a Ps1 CD. I would recomend you to get an ISO as i tested them myself and they work fine (the ones ill give u a link for). An ISO in fact contains all the information taken by a cd into one single file. After you download the ISO, you run it with the ePSXe 1.5.2 and the game should start.
Playstation 2 emulations are still in development. They can run final fantasy x but they are very slow and the game is not full playable (it crashes some time after you start) so i think you would waste your time trying to play it on pc.
Link to get ePSXe 1.5.2:
http://www.epsxe.com/download.php
Link for the ps1 plugins files:
http://www.vtemulation.net/utilities/plugins-psx.php (epsxe has its own plugins but if you have any problem with them you can find others from here. I suggest P.E.Op.S. and Pete's ones)
Link for ISOs: I would give you emuparadise.org but for some strange reason it loads very slow on my pc. Try this link:
www.emuparadise.org/roms/psx I dont know if it works though.
Iam sorry, you need to find bios files urself.
NOTE: Downloading a rom/iso of a game without owning the original one is illegal. Do it at your own risk