£250 upgrade ideas sought

OK! First off, Hello I'm Popeye, pleased to meet you.  

I got into pc's less than a year ago, with an old p4 rig. I outgrew that kinda quickly, and, got my current set up. (should be in my sig but ill list anyway)

ECS mcp61m-m3 skt am3 the only mcp unlock board in the world! (i can see why)
amd sempron 140 2.7ghz
2x2gb RAM (unmatched)
nvidia geforce 6150se nforce 430 integrated graphics
500gb seagate sata2 hdd
no name case and psu
pci trust 5.1 soundcard
no name case with unmarked psu ????
originally brought as a complete unit from websystems Nottingham (not by me)

anyway i had a car crash last year, and, have just been offered a settlement that im taking. Which leaves me with some money to put some of my affairs in order and make some much needed upgrades in a lot of areas,- car, kitchen,pc etc.
so i have allocated£250 possibly £300 to get my pc as good as i can get it, ideally able to play gta 4 and dolphin emu at reasonable fps

my mo bo is advertised as a core unlocker but it doesn't and as having over-clocking options wich it doesn't i am however assured that if i put a black edition cpu in with an unlocked multiplier these options will appear (they came up once in bios but never again) so i dont know whether to get a cpu for my mo bo or a bundle from ebay...to much choice to little knowledge!
i thought these two deals look good

http://www.ebay.co.uk/itm/Motherboard-and-CPU-Bundle-AS...

http://www.ebay.co.uk/itm/ASRock-970-EXTREME3-Motherboa...

but am open to all advice so £250-£300 absolute MAX to up grade what I have to browse convert video and game......any thoughts?