You'll want the Battlechest. This provides the base game, Burning Crusade, Wrath of the Lich King, Cataclysm, Mists of Pandaria and Warlords of Draenor (current expansion).
If you want to play US/Oceanic/Latin American Realms:
https://us.battle.net/shop/en/product/world-of-warcraft
If you want to play EU/Russian Realms:
https://eu.battle.net/shop/en/product/world-of-warcraft
A new expansion, Legion, is coming out shortly (end of August). There's no need to buy that unless you enjoy the game and want to continue playing it.
It's not really similar. WoW is an MMORPG, so there's generally a couple hundred players (or thousands on larger ones) online simultaneously per realm/faction, and there's hundreds of realms - and you can do almost all the content with anyone from any other realm. It's open world that's full of quests, dungeons, PvP activities, professions and many other social activities. It's one of those games that you can spend a couple of hours per week playing, or 12 hours a day playing and you'll always find something to do.
To get some more examples, you can just search World of Warcraft [raiding, pvp, any other term really] in YouTube.
Windows XP will work. WoW is
incredibly forgiving in terms of system specs. You can find those here:
https://us.battle.net/support/en/art...arcraft-legion
Upgrade couldn't hurt though. It's very old at this point and Microsoft no longer supports it, and Blizzard probably won't for much longer either.
There is also only one "version of the game". Everyone plays at the latest version, since it's an online only game. The expansion packs you own only determine the content which you can access.
Also, Blizzard has recently began publishing a whole lot of information for new or potentially new players here. It's worth a read:
New to World of Warcraft? Welcome Home! - World of Warcraft