The Advent appears OK, except for the weak graphics. So I would install a GT240 / HD4670 as mentioned in the other thread for ~£55 - purchase links with free delivery (if you choose it at checkout): click here / click here respectively. The GT240 will have a slight edge.
For ~£475 in total that's not too bad at all.
Btw, where does it say that it's £419 w/o Norton?
Another similar PC to consider is this Dell Inspiron 570 for the same price click here & 2-year warranty. Again get a separate graphics card as above.
The CPUs of the two PCs compared - if you'd like to have a look click here. G