My Photoshop 7.0 is configured for AdobeRGB(1998) as working space, and I am using Epson's generic ICC printer profile for the 890.
In Color Mode I, the files from the camera are tagged with an sRGB profile, and the colors come out OK on the Epson.
In Color Mode II, the files from the camera are supposed to be tagged with a profile (Nikon RGB?) which is supposed to have a wider gamut, but the colors in the prints appear somewhat washed out and with less saturation.
A) Mode II is Adobe RGB. If you have firmware 2.0, the image will open in Photoshop and be recoginzed correctly. If you have an older D100 firmware version you have to "convert" to Adobe98 when opening the image.
B) The generic printer profile is not going to give you the best results. Use the profile for the paper you are printing to, and disable the Epson "auto correction" features (see links below)
Actually, I have one that came with my Epson 870. I'm not sure what other printers have these "Generic" profiles but they do exist. I think the idea is that they profile the epson ink used with the printer. It does not take into account the color shifts introduced by the paper.
...which is Adobe 1998 color space, you should discard the color profile and then ASSIGN the Adobe 1998 color space. When a copy of this image is saved it will be correctly tagged.
You have two choices for printer output, as Ian Lyons excellent tutorial outlines: You can use the Epson printer "generic" profile in the ICM color management mode, or you can disable ICM and print to a specific color profile for the type of paper used. The results of these two workflows are very similar, but the latter (with a different output profile for each paper) is just slightly better in my hands. If you want better control of color than this, you will have to invest in color management hardware.