Extremely slow. That normally indicates the graphic card and/or northbridge driver(s) are not working properly. I have not seen that particular issue in any recent nVidia drivers. You likely have ATI; if so, try the Omega drivers or revert back several revisions. Many report that the newer ATI builds are buggy at first. Download and install the most recent stable versions of your motherboard chipset drivers, and you might want to update your video card bios, if the readmes mention non-cosmetic fixes.
You should run DXDiag (START - RUN - dxdiag.exe), run all tests, then click "Save All Information", then copy and paste that entire file (it might be quite long) here. There are lots of combinations of hardware, drivers, DLLs, etc. that could account for it, but it is too diverse to make specific recommendations at this point.
But I am sure it is related to textures, and since your AGP Aperture is adjusted correctly (leave it at 128 for RTW), you need to say exactly what graphic card you are using, including memory timings, overclocking (if any), and RAM.
Are you running a dual-core? If so, switch a core off.