As a proud owner of the 3805, I'll certainly commendate you on your selection of AVR. The 3805 is a workhorse knockout! Very feature-rich and connective. Running video through the 3805, whether it's an HD component feed from a cable box or from your DVD player or feeding it S-video from a VCR, is an easy and convenient thing to do. I run all of my video sources through my 3805 except for my 3910 when I'm using the DVI connection. Being able to switch audio/video sources at the same time is very user-friendly. However, when you get into DVI or HDMI switching within an AVR, you're talking serious coin. If you've got one HDMI or DVI source (such as a DVD player or HD STB), I'd run it directly to your display. If your display has more than one digital video connection, as many new sets have, then you're able to connect more than one source. Otherwise, you'll have to pick up an HDMI or DVI switcher to do the switching for you. Don't worry, there not very expensive at all.
As a quick aside, if you're really into audio/video, you may want to spend the extra $$ and get the Denon 3910 instead of the 2910. The video section is notably better and the audio performance of the 3910 is nothing short of stunning. Additionally, the 3910 is equipped with DenonLink (as is the 3805), for a one-cable solution (assuming the SACD approval goes through as planned).
Good Luck!
Jason