If you are planning to buy a separate card it wont be compatible with the Nvidia card, it wont run side by side and you will need to buy better components if you wanted two card running side by side (Of the same brand and preferably model)
The spec you have no chosen will be fine but dont forget the silver warranty.
You wont have enough budget as you would have to sacrifice a components to afford a better motherboard.
If you want to upgrade later you need to increase your Budget a bit to allow for upgradable parts.
Ok so this is my final rig spec
I was wondering about OC it and if the PSU or CPU cooler should be better... I have some OCing exprience and only want a moderate boost of about 500 to 600 Mhz
'
Case
STYLISH PIANO BLACK ENIGMA CASE + 2 FRONT USB
Processor (CPU)
AMD PHENOM II X4 955 (3.20GHz/8MB CACHE/AM3) - BLACK EDITION
Motherboard
ASUS® M4A78LT-M: mATX MAINBOARD, DDR3, USB 2.0, SATA 3.0Gb/s
Memory (RAM)
4GB SAMSUNG DDR3 DUAL-DDR3 1333MHz (2 X 2GB)
Graphics Card
1GB ATI RADEON™ HD5770 - DVI,HDMI - DX® 11
Memory - 1st Hard Disk
500GB SERIAL ATA 3-Gb/s HARD DRIVE WITH 8MB CACHE (7,200rpm)
1st DVD/BLU-RAY Drive
24x DUAL LAYER DVD WRITER ±R/±RW/RAM
Memory Card Reader
INTERNAL 52 IN 1 CARD READER (XD, MS, CF, SD, etc) + 1 x USB 2.0 PORT
Power Supply
450W Quiet 80 PLUS Dual Rail PSU + 120mm Case Fan (£29)
Processor Cooling
SUPER QUIET 22dBA TRIPLE COPPER HEATPIPE CPU COOLER (£19)
Sound Card
Ok so this is my final rig spec
I was wondering about OC it and if the PSU or CPU cooler should be better... I have some OCing exprience and only want a moderate boost of about 500 to 600 Mhz