I had never overclocked before i did a mates the other week but i can assure you its a simple and interesting process, learn a lot about how componants rely on each other etc. Using clunks guide and another guide i found specifically for the gigabyte DS3 boards it really was a doddle! If your embracing the geeky side atm its deffo worth a crack, you dont have to push the boundrieds at all just go for a reasonable speed.
If they case you said you might be abel to get doesnt become available then this would be my suggestion...
And do a modest overclock to about 2.5 - 2.8 which is easily do-able
If you can get a case then spend the extra dosh on a better cpu/ram/mobo... suppose you could get the PC6400 ram anyway as there is £20 quid left within the budget
If you really dont want o overclock then get a lesser PSU and maybe just go for AMD as you will get better performances with stock levels for the price.