The normal professional solution is to place gels (big plastic filter sheets) over the external windows.

Since the actual interior lighting is usually a feature of architectural photos, additional lighting inside is normally balanced to whatever the existing lighting is (often tungsten or "warm white" fluorescents). If you are adding additional light, that usually means using a CTO (Color Temperature Orange) gel on your flash.

Natural lighting outdoors is not only too bright at midday, it's also usually way cooler (a higher color temperature) than the lighting indoors. To compensate, you'd tape or tack CTO gels (which are available in large rolls) to the exterior of the windows, often along with a neutral density gel (or a combined CTO/density filter). Depending on the time of day, and on whether it's north or south light, you'd need to use a different "cut" of CTO (a different strength of orangeness).

If that sounds like it's troublesome, expensive (in terms of man-hours) and would go much faster with a color meter and a production crew, you're right. It's a lot easier to go the multiple exposure route -- just make sure that you are using a good tripod (or two -- one on the lens and one on the body if the lens has its own ring; the second tripod doesn't need to be heavy-duty, since it's just a stabilizer), a remote release and mirror lock-up. Current good HDR-capable image processing programs should be able to do the pixel matching, but you'll likely have some color correction to do to make the exterior exposure match the interior.