upgrading hardware aurora alx

hi there

i want to upgrade a few things on my desktop

i want to replace the harddisk
for an ssd disk OCZ VTX3-25SAT3-240G
i have readed lots off that the disk won`t have the right speed.
the needed somthing else a cable or something to get the right speed from the ssd is this correct?
or what do you recommended for an ssd disk to place in my system? that have space about min 120 GB max 240 GB

and what kind off graphic card will fit in my system?
i see lot of high end graphic cards. but i dont now what to buy because i dont now how many watt of power is recommended whit this system
AMD Radeon™ HD 7970 Graphics like this one. is this one possible? and will it work maybe in crossfire x. it just an example.