The cpu you have is an APU, that means it is a gpu and a cpu on one die. (in one processor chip) It's kind of a a waist to use a 7750 with an a4-3400 because of that. Either get a radeon HD 6450 graphicscard and crossfire it (dual gpu mode) with your apu or buy instead of an Apu a CPU such as the Athlon x4 641 (uses the fm1 socket too). Otherwise you're good
You just put the card into into the computer (only works with radeon 6450 when using an a4 apu). You probably have to update the bios so this is possible. As much as I can remember you have to then enable something called "igx or igfx or something like that multi-monitor". Then when you boot catalyst control center should pop up and tell you that crossfire is available. Only do this after you indtalled winodws with all the drivers properly.
Also, enable ahci sata mode for the first 4 or 3 or 2 sata ports. Plug your odd into the last sata port (before you install windows). Don't forget to load the ahci drivers from the mothrboard cd when installing so the drive gets recognized. Ahci is much faster comparing to ide mode because it supports ncq and other features as long as your harddrive also does.