I took this photo recently w/ an old Pentax K1000, using 400 ISO film, and an f/1.7 aperture. Is this graininess just inherent to shooting w/ this sort of film / lighting? Or, is it partially/largely caused by the scanner that scanned my photo?
In other words, is this just how it's going to be no matter who scans my photo? Or, should I be looking for a different place to get my processing done?
ISO 400 film is almost always going to have grain that's at least somewhat visible. I can't really tell if you underexposed the picture or not, but underexposure will generally make the grain much more apparent.
Different scanners show grain to (slightly) differing degrees. Basically, the smaller the light source, the sharper a rendition of the finest details it'll give -- and the more apparent the finest details like grain will be. A larger light source "softens" the scan a bit, which tends to make grain slightly less apparent. Unfortunately, if you're getting the scans done commercially, you may not even be able to find out what sort of scanner they're using, not to mention getting them to select a different one that's more suitable for a particular picture.
Scanners are effectively digital cameras so they do introduce noise but not very much, what you're seeing is the film grain. ISO400 film is very grainy when compared to ISO400 on a modern DSLR. This often gets forgotten when comparing film to digital (resolution or otherwise).
Grain aside (which as already stated isn't always objectionable) the photolab scans are pretty poor quality all round. Getting a professional drum scan may not improve grain but will probably result in better colours, dynamic range etc.
I'd guess that 400 ISO film is grainy.
(I think it looks nice!)
What is the resolution you're scanning at? The issue really is this: no matter how high-res your scan is, a grain will always be smaller than a pixel, so for something that you want minimal grain, scan at the highest resolution the scanner can give. Also take note that contrast and sharpness adjustments in post tend to emphasise grain, so that's another thing to watch out for.
Did you push the film? I'm going to say that grain is a part of film and for 35mm negs, it is rather difficult to not have them when they are scanned.
You could reduce film grain by using wet mounting (immersing film in fluid) during scanning, if your scanner allows it. It would also help with saturation.
