I have made a
blog post about this. However, I know not everyone that knows me online reads my blog, so I figured, "what the heck" I'll post about this and answer this question.
Okay, if you notice my gamer card, it has Yuri as my gamer pic.


The left one is a still version of my gamer card. The right one is linked to my actual gamer card.
Well, last night, I was messaged about it by Kaji while playing Resident Evil 5, which lead me to decide to post about it outside of my blog. Also, someone else sort of reminded me to do so by asking himself (I couldn't explain in details to either one on Xbox Live, so the details are here).
Of course, these gamer pics aren't on Xbox Live Marketplace. Where did I get them?

I had to track down a back issue of OXM on eBay (it's the Holiday 2008 issue/OXM Disc 91).
It's part of the bonus content in said disc. Also, they aren't going to let you install it so easily. You'll have to run the demos at least once (that doesn't mean you have to play it. You just run it.) so that the OXM points from said disc are at least 800. After that, you can unlock the gamer pics and install it for your use.
Now, these are what they look like:

Yuri, Flynn, that Tales 10th Anniversary medal, Estelle, and Repede. If you were hoping for Karol, Rita, Judith, or Raven, well, I haven't tried it myself, but you could try faking it if you have an Xbox Live Vision cam, since I remember hearing you can take a picture with that and use that for your gamer pic.
That's pretty much the thing with how I have Yuri as my gamer pic, despite Tales of Vesperia gamer pics not being on Xbox Live Marketplace. Figure I do this to answer a question before it's asked one more time.