1. As a way to get started quickly (i.e., without programming), you might like playing with graphical ROM hacking (with YY-CHR, for example). This is an easy way to become familiar with the graphic format of NES games. Check out romhacking.net for more information on ROM hacking.
2. NO CARRIER's glitchnes and NESFlix and blargg's litewall are awesome NES visual programs that require little to no programming experience and are well documented. The great thing about these ROMs is that they're really suited for visuals, and you'll be able to add your own graphics using a program like YY-CHR. I tried out NESFlix recently, and I was able to make a ROM from an animated GIF in under 30 minutes (!).
3. If you're looking to make truly custom visuals and willing to devote some serious time to learning 6502 assembly, I would recommend the NES programming tutorials on the Nintendo Age forums. (In my opinion, NESDev is not the absolute best place for beginners.)
Best of luck to you!
]]>And you can of course create a ROM yourself.
Coding for old systems is a ton of fun, but also quite the challenge and can be very exhausting.
You need to learn a language suitable for what you want to do (ie: C, Assembly)
And you need to learn about the hardware, and the tools to compile for it.
Set aside an hour to google about all this.
You'll get a more clear sense of what you can or cannot do, and what you need to learn in order to do so.