Here is the full list of all 45 Final Fantasy VIII achievements. It takes around 100-120 hours to unlock all of the achievements on Windows.
Finish the game
Finish the game with Squall's initial level
Beat the Omega weapon
Kill 10000 enemies
Complete the Obel Lake side quest
Complete the PuPu side quest
Learn all of Quistis' limit breaks
Unlock Guardian Force Eden
Unlock Guardian Force Bahamut
Collect all cards
Reach level 100
Unlock Guardian Force Cactuar
Draw magic 100 times from draw points
Find Ragnarok
Reach level 100 with Boko
Unlock Guardian Force Doomtrain
Acquired an item from Chocobo World
Capture a Chocobo
Unlock Guardian Force Tonberry
Kill 1000 enemies
Collect all Weapons Monthly/Combat King/Pet Pals/Occult Fan magazines
Collect all Timber Maniacs magazines
Learn all of Rinoa's limit breaks
Unlock Guardian Force Alexander
Unlock Guardian Force Cerberus
Defeat every member of the CC Group
Win 100 games of Triple Triad
Lose a rare card in a Triple Triad game
Unlock Guardian Force Pandemona
Unlock Guardian Force Leviathan
Reach maximum HP
Unlock Guardian Force Carbuncle
Reach SeeD rank A
Reach maximum Gil
Unlock Guardian Force Brothers
Upgrade your weapon
Unlock Guardian Force Diablos
Draw (Stock) magic from enemies 100 times
Kill 100 enemies
Get your first salary from SeeD
Play Triple Triad
Unlock Guardian Force Siren
Unlock Guardian Force Ifrit
Unlock Guardian Force Shiva
Unlock Guardian Force Quezacotl