Socket 775 is a thing of the past, I wouldn't go that way. At today's prices, you go or i7 or Phenom II, at your budget you'd go Phenom since it'll bring you the best bang for the buck. The C2D your looking at has two cores, the Phenom I'm proposing you has three; better multitasking and if you're like me, forgetting to close all your programs before you play some games, you won't be slowed down if there's a background process since it'll be offloaded to the third core (assuming you wont be playing one of the 2-3 games that uses more than two cores), it overclocks very well and if you ever want to make an upgrade to your system, you can do so for the next few years to come since the AM3 socket is new. The board has an integrated video card which is not great but not completely crappy, if you're missing some money for now, you could cut there at still play all your games on minimum until you get your next paycheck.
At a later time, you can get a second video card to boost your performances, or add a professional sound card or whatever other card that uses a PCI-Express slot.
So I'd say go with an
Asus M4A78T-E for £105 and a
Phenom II X3 720 Black Edition for £120
You'll end up with a better deal with an
HD 4770 at £83 with free delivery, because you could put a second one at a later time in your board and also since it's the best card for the money you can get today.
Antec 300 is a cramped case with bad airflow compared to the
Cooler Master 690 that comes at £64 with free delivery and for a small fee you get a tee-shirt

(just saying...)
I agree for the PSU unit, since you'll have more than enough power with it, OCZ is a good PSU brand, and at £45 you're good.
http://www.ebuyer.com/product/135159
The hard drive will be filled up pretty fast and this
Western Digital Black Cavier 500GB with 32MB of cache is faster and bigger at £52.
For the RAM you'll need DDR3, which will become cheaper and more accessible than DDR2 in the next months, so you can start off with an
OCZ 4GB kit of PC3-10666 for £55
You don't really need a CPU cooler for now, it's an investment you could do, but it's not necessary, I've been running a big overclock (1.8Ghz to 2.8Ghz) on my stock cooler for over 2 years.
As for the DVD drive, it really doesn't matter in my opinion, you just get one you like, I have a preference for LG after testing Pioneer and Sony and disliking them for the loudness of the drive.
As for the screen, I have it and I hate it pretty much, it's small, you can't see a full document page, and the difference in price between this one and a 22" is minimal, I'd say go with a 22" if you can afford paying £20 more, for example this
LG W2234S for £110 or if you don't mind having a small screen a big resolution (which gives you a better image quality perception) I would recommend
BenQ G2220HDA, it has a FullHD resolution = 1920 by 1080, and at £110 it's a steal. With that screen you can basically put two Word 2007 documents next to each other and be able to see the full page.
I don't know if the £50 over is ok, but I believe it's the best investment right now that you can do.
Total of £650