As he's not going for big resolutions you could get away with these
600w psu. Gives you room to upgrade the rest of the system at a later date. Never by a cheap unbranded psu. If a psu dies 9 times out of 10 it will take the whole system with it.
http://www.overclockers.co.uk/showproduc...amp;subcat=1084

This gfx card should give you decent performance. Its nvidia but i don't know my way around the ati range
http://www.overclockers.co.uk/showproduc...914&subcat=
Little bit over the £100 mark but will make a huge difference to his system!

This is the card i use and will cope with anything i throw at it
http://www.overclockers.co.uk/showproduc...amp;subcat=1830