Those cheap Inspirons are very good value - with the caveat that you're getting what you pay for...
For an "occasional use" or second PC it should be alright, but i wouldn't leave any valuable data on it.
A couple of things though;
The 768MB RAM offer ends today
The price you've shown only includes a
90 day collect&return warranty. I've seen a suggestion on another forum that this isn't actually legal, as you could reasonably expect a laptops life to be more than 3 months, so you've really got two choices. Either suck it up and pay another £100-ish for the 3-year warranty, or take the 90-day bollocks and try and argue your customer rights if it breaks down too quickly. Of course you could be lucky and have no problems, and for £400 for a reasonable laptop you might decide it's worth the chance
Oh yes, it is this one isn't it?
http://configure.euro.dell.com/dellstore/config.aspx?cs=ukdhs1&kc=ukdhsonl&oc=N05136&x=0&y=0