Well, in C4D and most 3D applications, dpi is *sortof* meaningless. Here's how you get the end result you want:
For example, let's say you want an 8" x 10" image at 300 dpi. DPI being dots per inch, of course, so you need 300 dots (or in our case, pixels) for every inch. So you multiply 8 * 300 (which comes out to 2400) and 10 * 300 (which comes out to 3000) and so you want to render your image at 2400x3000 resolution. It doesn't matter if it's a tiff, jpeg, targa, png or whatever. Now when you bring that into photoshop, it'll probably default to 96 dpi (or something else) because all of those file formats don't support a "dpi" setting. After you've got the image open, go to Image->Image Size and *uncheck resample image* and change the resolution to 300 dpi. As long as you've unchecked "resample image", you're not going to actually scale the image up or down, you're just changing how photoshop views it. In this case, it goes from being 25x31.25 at 96 dpi, to being 8x10 at 300 dpi.
I know it's a little confusing at first, but dpi is primarily a "print" thing. An image that's 800x600 pixels can be either 8x6 at 100 dpi or 4x3 at 200 dpi. (because again, 8*100 = 800 and 6*100 = 600, as well as 4*200 = 800 and 3*200 = 600).
Anyway, I hope that helps you get the end result that you need.
DPI is definitely quite a difficult thing to explain clearly, I've yet to find an analogy to help describe how changing the DPI in photoshop without resampling actual only changes how OTHER applications see that image.