Hi, just had a look and you will not be able to have i5 for your budget. the second Argus link is for i3 which is OK if you are on a budget. If you look on the Dell UK website they do a 15" i3 Inspiron for £399, a bit more than Argus but a larger screen.
i3,i5,i7 processors are the good processors from Intel .processors are the chip which is basically the computer about the size of large postage stamp, the rest of the computer is so you can access this and store your data.
hope this helps