Believe it or not in this case the higher-numbered CPU might actually be lower performance. It's 200Mhz per core slower, as you can see on the specs, but does have a 2MB instead of 1MB cache. Larger caches only matter for certain kinds of workloads though, and in general do not come into play for average "office tasks". You can see a benchmark result comparison (for only one benchmark admittedly) here:
http://www.cpubenchmark.net/cpu_lookup.php?cpu=Pentium+Dual-Core+T4500+%40+2.30GHz
http://www.cpubenchmark.net/cpu_lookup.php?cpu=Intel+Core2+Duo+T6570+%40+2.10GHz
and a couple more:
http://www.notebookcheck.net/Intel-Pentium-Dual-Core-T4500-Notebook-Processor.25727.0.html
http://www.notebookcheck.net/Intel-Core-2-Duo-T6570-Notebook-Processor.34898.0.html
Note that in those benchmark results, SuperPi is one of the few places you'll see the T6570 pulling ahead, most likely due to its cache.

Now, even if the "lower" CPU weren't faster in the majority of tasks, I'd still recommend more RAM, especially if you're getting Win7. While Win7 doesn't seem to require as much RAM as Vista, it still runs better with 4GB than 2GB. Combine that with the fact that the first option is cheaper, has more HD space, and a memory card reader (dunno if it's important for you but I won't buy a laptop without one), and I think the choice is clear.

- Oshyan