From the excellent Half-Life 2 Stuttering Problem Page:
A solution for the stuttering problem has been found and a fix is coming. I’ve been talking with Gary McTaggart about this today and it turns out that my texture management theory was correct. A patch will be coming for this issue that will load all of the required textures into video memory on level load, rather than doing it during game play. There is currently no ETA for this patch, but I will post an update as soon as I get more information.
Excellent news 🙂
We’ve found a fix for this problem, and we’re planning on shipping it no later than tomorrow.