One more thing. Note the list above is ONLY for Intel Core 2 Duo CPUs.
Intel do make a number of other CPUs and it can be very difficult for anybody to sort them out.
Below is a list of laptops from the Dell site and it may be useful for you to see the different CPUs used in each to get an idea of the different numbers.
http://www1.euro.dell.com/content/products/res ults.aspx/notebooks?c=uk&cs=ukdhs1&l=en&s=dhs& ~ck=mn&page=1
Note the first laptop in the list (Inspiron 1525). It says it has a Intel Celeron Dual Core T1400. So this is a "dual core" but uses the Celeron brand name for low end CPUs. That laptop is only �369.
Note the 5th laptop in the list, the Studio 17. This has a Pentium Dual Core 2370 (dual core but with the Pentium brand name). This laptop is �499.
So neither of these are "Core 2 Duo".
Note the 3rd laptop on the list, another Inspiron 1525. This has a Intel Core 2 Duo T5550. The laptop is �429.
That CPU is on the list I gave you above, but is fairly near the bottom so is less powerful than others higher up the list.
Finally if you look at the 8th laptop in the list, another Inspiron 1525. This has a Intel Core 2 Duo T8100. The laptop is �579.
That CPU is also on the list I gave you above, but is near the top so is more powerful than others in the list, hence the higher price for the laptop.
Sorry for the long append, but you can see how Intel have a bewildering array of CPUs so sorting them out is not easy.