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