For a few years I've been playing Oblivion on my ps3 but recently I just bought a new laptop so I plan to install the PC version, and I was just wondering
what KOTN came with? Is it just the faction or does it come with the other plugins as well? (Wizards Tower etc)

PC GOTY is just Oblivion, KotN and Shivering Isles. No extra DLC. By the way, if/when you install it, don't worry about "getting the latest patch" as many recommend on the mods sub-forum. PC GOTY, once everything is fully installed, will be up-to-date (or at least as up-to-date as you're gonna get) including the latest patch (which isn't so recent). There are player-made Unofficial Patches which further correct glitches, but that's a subject best handled on the Mods sub-forum.

-Decrepit-

Do you mean the Knights of the Nine expansion disc? Or the Oblivion GOTY? I have the GOTY, and it came with Knights of the Nine and the Shivering Isles, but none of the other dlcs. I believe the separate KOTN disc comes with it and all the DLCs except Battlehorn Castle. But no Shivering Isles. My recommendation would be to get the GOTY, and then download any of the DLCs that look interesting to you from Bethesda's site.