An external HDD isn't going to do anything to improve your performance. The only relation to ram would be extra swap space, but there's really no performance gain to be found in additional swapped memory. Add more ram if you can, although in my experience most components for laptops tend to be too inflated price wise to make it worth it.
Dual core processor
2.26GHz 2.27GHz (Why are there 2?)
Read the line preceding the one where you ask "why are there 2?", and pay attention to the first word.
Modern PC's have multiple processors housed in a single slab of silicon. The two figures are the (approximate) speeds of each processor.