Do I add the 2008 R2 32bit driver?
Não existe tal coisa.
Do I add the Windows 7 32bit driver? Since I have XP and 7 I don't know which x86 driver to add?
Normalmente, os drivers de impressão não são específicos da versão. x86 Win 7 drivers normalmente funcionam bem para clientes XP.
Strangely - and maybe this is case - I have downloaded a printer driver for 2008R2 64 bit - and extracted it - added a printer using the 64 driver on my server VM, then added the additional driver for my 32bit version - and still my XP and 7 Clients can use the driver? Do the Server drivers (2003 and 2008) contain all OS' drivers or does it not matter which OS platform you get for the driver, just any 32bit driver will do?
Isso é normal, embora normalmente os drivers x86 Server 2008 ou 2003 sejam um pouco mais desatualizados do que os drivers x86 W7 para o mesmo modelo.