Most of the time, when I approach a NPC, right before he/she starts talking, there is a very short freeze (fraction of a second) and then the game resumes as normal. Very annoying. Anyone else seen this?

Core2 Duo E6750, Win-XP, 3 GB RAM, Geforce GTX460.

Skyboost or no Skyboost, the tiny freeze remains. Is it perhaps the game retrieving the voice-file from HDD?

Nobody else?

This is an issue I experienced in mount and blade series. I think though in your case is simply an issue of raw power. Try exiting all the aplications you can before running skyrim. Using gamebooster (an aplication doing this automatically) could help you greatly.

"raw power"...huh? Power of what? CPU, RAM, GPU, HDD? And why are the voices of the NPC's in Oblivion, FO3 and FNV ok then?

Sorry, I mean RAM. This game is less hardware stressing than previous ones, but the RAM usage can go to the rof easilly. That's what I suggest you to exit all the unneded programs you can, that could help and if not at least you will know that the RAM is not the problem.

By the way, I didn't mean you haven't enough physical RAM installed I have only 250 Mb more than you and have no problems at all, so 3 Gb should be enough while you didn't have too many processes in the background.

FONV ini had this -

[BackgroundLoad]
bBackgroundLoadLipFiles=0

You can try adding that to SkyrimPrefs.ini and changing it to 1 and see if it helps.