If you buy straight from the company (like HP or Dell), you will have more customization options, but you will be slightly limited in warranty options. I don't know how important the warranty is to you or not. Centrino 2 is not actually a specific chip but a term covers a particular combination of mainboard chipset, mobile CPU and wireless network interface in the design of a laptop. Either way, you will still be getting a Core 2. Unless you can't live without a laptop the first few months of fall semester, I would try and wait until October, as that is when Intel is supposedly releasing their new line of laptop processors. Regardless, I would try and wait until August as that's when they have all of the back to school specials on laptops and you can usually get an amazing deal then.
It really depends what you plan on using the laptop for. Whether it's general to moderate gaming or just note taking and web surfing. It can make a big difference as to what is best for your needs.
There's always a workaround........