ok, anything new on a single core processor is going to run slow, that's a given but the best upgrade he can make is still a gpu upgrade, then a memory upgrade, then a cpu upgrade. rating by biggest gaming improvement first. cpu's aren't as detrimental to gaming as a graphics card is and if you have a low amount of memory (2gb or less these days) that will impact texture loading and have other issues.
however it's not a bad idea either way if he's going to upgrade both the cpu AND gpu, it doesn't matter which one he upgrades because it's going towards a target and not a "which will give me better performance"
the cpu and ram would be a big upgrade for windows performance, program loading times, texture loading times, overall increased loading times and processing times but as far as graphics go his maximum fps wont increase very much.