Hi guys - first off, just wanted to say thanks - I came here on my first ever build a few years back, and the advice you gave me helped me build a great low-budget rig, had absolutely no problems with it - and thanks doesn't get said enough around here. 
While still solid, my PC is getting on a bit now - so I thought I'd drop a bit of cash this Christmas on upgrading a few components. I'll just pop the old spec below in a quote for reference.
I'm thinking of dropping about £200 quid (with a fair amount of leeway) on upgrades, so I was hoping you'd be able to recommend what my money would be best spent on. Putting the graphics card aside (most likely I'll upgrade that later) I was thinking of picking up a new Mobo and CPU (possibly alongside a new PSU if you think i'll need the extra power).
So - can you suggest some components along those lines, and am I looking in the right direction?

While still solid, my PC is getting on a bit now - so I thought I'd drop a bit of cash this Christmas on upgrading a few components. I'll just pop the old spec below in a quote for reference.
Radeon HD 4870 512mb ("dark knight")
Gigabyte GA-EP43-DS3L Intel P43 (Socket 775) PCI-Express DDR2 M0otherboard
Intel pentium Dual-core E5200 "LGA775 Core 2 2.5ghz (clocked@3ghz)
Antext Earthwatts 500W PSU
Antec 300 case
Western Digital Cavier Blue 640GB SATA-II 16mv cache OEM Harddrive
OCZ 4GB (2x2GB) PC2-6400C5 Duel Channel Vista Gold series DDR2 RAM
Artic Cooling Freezer 7 pro CPU cooler
DVD writer, soundcard etc
I'm thinking of dropping about £200 quid (with a fair amount of leeway) on upgrades, so I was hoping you'd be able to recommend what my money would be best spent on. Putting the graphics card aside (most likely I'll upgrade that later) I was thinking of picking up a new Mobo and CPU (possibly alongside a new PSU if you think i'll need the extra power).
So - can you suggest some components along those lines, and am I looking in the right direction?