New Build/Extreme upgrade

Hi there, i'm new to the forums, but i've broswed around alot before. Currently I have
AMD athlon 64 3200+
Asus a8n5x motherboard
500GB SATA barracuda 7200.12 HD
1GB DDR ram
Radeon HD5450 video card
500w power supply
2 case fans in ibuypower full case ATX
I got this computer when my fiance's parents upgraded recently. I put 1GB ram in up from 512MB, put in a new dvd-burner(SATA)and 500GB HD(SATA) and last year the Radeon HD5450

This was all before i knew the specs for FFXIV So now i'm looking at getting a new MOBO
ASRock AM3 processors AMD 770-140W 4DDR3/ATI CrossFireX motherboard

CPU
AMD Phenom II X2 555 Black Edition Callisto 3.2GHz (possibly unlock to x4 if possible, but for gaming i've read it might be better to run it x2 but OC a little more)

and DDR3 RAM
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600

This will be my initial upgrade until I can save up another $100-200 for a sufficient video card, i'll throw my Radeo HD5450 in until then. And I'm just going to use the hard drive, dvd, and hopefully power supply for now. Is this feasable? Do i need to upgrade the power supply now? Will I when i get a new video card? I'm looking at the 5670 video cards look like it should do. I don't need max resolution i still have a VGA monitor. I just want smooth fps at medium res. Any comments are much appreciated. Thanks

-Tyler