[Druchii]

I see two main differences, they are as follows:

One processor is a Pentium Dual Core, which although probably powerful enough to watch DVD's iPlayer content and of course do just about everything bar game or crunch any real numbers (Think encoding or rendering). The other, is a Core 2 Duo, which are amazing processors, these can do everything, even at the relatively low speed of 1.66Ghz.
So, it's low-range that can do almost everything you can throw at it, or it's mid-to-high range which can do everything you throw at it without breaking all that much of a sweat.
If you want to know the main differences between Pentium Dual Core and Core 2 Duo, it's the processors cache (the bit the processor can read and write to really really fast, and where it stores common stuff for the application it's working with right now). The Core 2 Duo has double the amount of the Pentium Dual Core if i remember correctly.

The other difference is the hard drive space, 160Gb vs 250Gb, i think you know what this means though. (storage space).

Another thing to consider, is how long you plan on keeping this one without upgrading? Is it worth spending that little bit extra now, to save you wanting a new one in a year?