If it is just distant objects, it sounds like you rig is have problems keeping up with the game. Make sure anisotrophic is set to bi or trilinear and no AAliasing. If you are still having problems, run the game in DX7 mode.
-dxlevel [version]: Using this command allows you to force Half Life into only using the specified DirectX version for shaders. For example, use -dxlevel 70 to force Hardware DirectX7.0 level support for shaders. This means a reduction in image quality but an increase in performance. Other values include -dxlevel 80 -dxlevel 81 and -dxlevel90. Note that this only works if you choose a DirectX version which is lower than the current one supported by your graphics card. See the Hardware DirectX Version option under the In-Game settings for more details.
I had the same problem with my geforce 2. The solution I found suggested elsewhere for a similar problem was to downgrade the drivers, due to the age of the video card. The most recent drivers I found which didn't cause this annoying problem were Nvidia's 43.45 version, released in 2003. The driver archive page for windows xp/2000 is here: