Please forgive me for any lack of information. I deal with Intel and NVidia (myself) and have ventured into unchartered territory, in an attempt to help the girlfriend's younger brothers have a half decent system, capable of some gaming.
The desktop is a - HP Pavilion p7-1449 Desktop (see link for details)
It is currently fitted with the "AMD Radeon HD 7660D Discrete Graphics." I actually thought it was integrated/chipset based? Anyway, they can do some gaming such as League of Legends and WoW, but they would like to play some of the newer games such as BF3 and GRID2.
I was thinking about purchasing a 7850 as they would see considerable performance increase and it wouldn't break the bank (and should somewhat 'suit' their overall desktop specifications)
EDIT - Included a couple pictures.
Do I need to upgrade the PSU?
Is it a straight swap/install?
Will it be sufficient for their requirements?
Anything else I should note with this upgrade?
Thanks in advance.