Okay i got Proph and GWEN... and i need to buy Faction because in some reasons...
What happends if i buy GuildWars Platinum? And i enter the key? Is that okay?
Even when i already got Proph?
*SRRY PEOPLE... I mean the Platinum Proph and Factions on it...
Help Me Out!!!!
Christian-D_D
Etta
Hold on, Guv. You said you already have Prophecies and Eye of the North and you need to buy Factions, right? Then why would you want to buy GW Platinum?
KoKoS
If by gw platinum you mean the 1million edition, it's ok, because it'll just unlock some items for you.. 
Christian-D_D
SRRY PEOPLE... I mean the Platinum Proph and Factions on it...
Darcy
Guild Wars Factions Platinum Edition (found on the wiki http://wiki.guildwars.com/wiki/Factions )
Guild Wars Factions
Guild Wars Prophecies Game of the Year Edition
Guild Wars Bonus Mission Pack
Installing a campaign that you already have won't change anything. I think it refuses to accept the access key unless it's a different version (such as Game of the Year). So you would add the keys for Factions, GotY and BMP. This would give you Factions, BMP and the extras for Prophecies without affecting your current install.
All your info is kept on the ANet server and is tied to your account.
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Edit after research
Guild Wars Factions
Guild Wars Prophecies Game of the Year Edition
Guild Wars Bonus Mission Pack
Installing a campaign that you already have won't change anything. I think it refuses to accept the access key unless it's a different version (such as Game of the Year). So you would add the keys for Factions, GotY and BMP. This would give you Factions, BMP and the extras for Prophecies without affecting your current install.
All your info is kept on the ANet server and is tied to your account.
===================
Edit after research
Masseur
Factions is $19.99 on newegg.com by the way, so is nightfall