If given a choice between a single or a dual core, then get the dual core. Dual core CPUs are the best on the market (actually, quad core are, but multiple cores = good). Basically, instead of one CPU doing everything, a dual core chip has one CPU piggybacked on top of it, so when its doing severa things it can delegate some tasks to the other CPU. In essence, it doubles efficiency. Speed becomes less of a factor because if I have something running slower but that can handle more then I still have a good balance.
That said, single core machines are much cheaper. If you want to get a faster machine then spend the extra 100 or so and get a dual core instead of a faster single core. The machine will last you much longer and work much better.
I just spent a good 30 minutes trawling my usual hardware suppliers - cant find anything better price wise than that one you want for 299... nice find. I do recommend that you put the make and model number into kelkoo, froogle and pricerunner and just google it to, see if you can find it cheaper anywhere else.
I would recommend that you avoid eBay for laptops. My experince of lappys on eBay is that most new ones are stolen and the others legitimate ones are simply overpriced.
Alternatively, you could just get a desktop. Buy a decent tower and to save money sacrifice the flatscreen. They are lovely pieces of kit but you can get a 17" or even a 21" CRT monitor off of ebay for ubercheap. I paid £40 including delivery on my 21" CRT and its awesome. The pixel definition is fantastic and its huge. If you want a flatscreen, then Aldi have a 17" flatscreen in stock right now for £130.00 and thats hard to beat. Its a Tevion brand, my experience with this brand is that its cheap but fairly high quality.
Open Office is great, but if you want to save money then its likely that
this particular search link will save you 100% cash, especially if you use Daemon tools and dont even waste a CD.
Quickie edit
Check your local large Tesco. Mine has got a great deal on the end of a line of Gateway stock, theyre £350 and dual core, I think with 512MB ram. Its not listed on the Tesco direct site though, these offers are store by store only it seems, but its worth a look. Bear in mind that I sell hardware online and recommending the biggest competitiors doesnt come easy to me
