To get the graphical improvements, go to the MOD tab in the launcher, click "Select MOD" and select the "mediavps" folder from the list that appears. Then, go to the "Features" tab and check "Enable specular", "Enable glowmaps" and "Enable environment maps". Now try running the game again, and see if that makes a difference

The graphical improvements are optional, you see, and have to be manually enabled. There are a wide varience in the quality of the systems people are running, and this ensures that even those with older computers can still play the game. I know it's a bit of a bother, but there you have it

[Edit] Oops, overlooked the launcher part. Version 5.5a is definitely a better choice than version 5, though the older version will probably work.