Resources I’ve found to help keep my Dell Latitude E6400 running optimally.
Parts Upgrade
Parts People do Dell really really well, you can buy direct or use their site to see what part numbers you need.
http://www.parts-people.com/index.php?action=category&id=140&subid=222
CPU/Processor Upgrade
You can see what your processor spec is like here http://www.cpubenchmark.net/cpu_list.php
Or do a search in Google and type something along the lines of Intel P8400 vs Intel P8800 and choose the cpu-world.com listing, this will let you know what the improvement in performance will be.