He could just about do it for £250 mate but not £200.
Intel E2160 Socket 775 Pentium Dual Core 2x1.8Ghz 800FSB Retail Boxed Processor
http://www.ebuyer.com/product/127248 £44.33
MSI P6NGM-FD GeForce 7100 Socket 775 Onboard VGA 8 channel mATX Motherboard
http://www.ebuyer.com/product/140209 £38.94
Hitachi 160GB Hard Drive SATAII 7200rpm 8MB Cache
http://www.ebuyer.com/product/124291 £28.83
Corsair 2GB Kit (2x1GB) DDR2 800MHz/PC2-6400 XMS2 Memory Non-ECC Unbuffered CL5(5-5-5-12) Heat Spreader Lifetime Warranty
http://www.ebuyer.com/product/98710 £32.00
Optiarc AD-7200S 20X DVD±RW/DL/RAM Internal SATA Bare Black Drive
http://www.ebuyer.com/product/139414 £16.00
Casecom 6630 Black Midi Tower Case With Front Panel USB2.0/Audio - No PSU
http://www.ebuyer.com/product/119589 £10.99
ATI HD 3850 Pro 256MB GDDR3 Dual DVI TV Out PCI-E Graphics Card
http://www.ebuyer.com/product/139597 £86.94
The above comes to £258.03
Now one problem is I have not added a PSU because eBuyer no longer sell my secret weapon!!! It was the SilverPower 350W PSU which were high end PSU's at a fantastic price!! I think they were just £19.99 which would be a little over your £250 budget but this setup would be perfefct for your dad.
All high quality componensts, that motherboard although it is only a 630i chipset does let you overclock and you should be able to push that processor up pretty high if needed. The ram is high quality stuff, the hard drive has 8mb cache and the graphics card is a bargain at less than £90!!
Now we just need to find a decent PSU, if you can find a SilverPower PSU a 350W will do you fine. But don;t by just any cheap crap mate, for £20 only SilverPower will do!!
An alternative for ram will be this:
OCZ 2GB (2x1GB) PC2-6400C4 Dual Channel Platinum Revision 2 XTC Series DDR2 (OCZ2P800R22GK)
http://www.overclockers.co.uk/showproduct.php?prodid=MY-072-OC&groupid=701&catid=8&subcat=
£24.08 + P&P
This for me is better ram than the Corsair and this version also has better timings. It is also cheaper but it means buying from another company and adding postage on top. But it should still cost less than £30 and would be my personal choice.
Also found this PSU on overclockers:
http://www.overclockers.co.uk/showproduct.php?prodid=CA-020-GI&groupid=701&catid=123&subcat=
Gigabyte SUPERB 460w PSU £28.19
I have done some research and it seems that this PSU is in fact a rebadged FSP which are one of the best in the business. Here is a detailed look at the FSP model.
http://www.fsp-group.com.tw/english/1_product/2_detail.asp?mainid=1&fid=52&proid=301
So all in all that looks like a good PSU for less much less than £30.
Also have a look at the 3800 series of graphics cards on Overclockers while you are there. They do seem to have some great deals on, especially some 512,b versions for less than £100 which are better than the 256,b versions. (I know that sounds logic but in some cases 512mb is worse than 256mb).
And they ar throwing in free games.