Depends how much you want to spend....
You can spend a lot and do something as posted above. Or you can spend as little as $2.00 for a soft, clear plastic sleeve... and put the nails through the plastic (and not the pennant itself).
Another cheap option is the rigid plastic sleeve. That would cost you about $3.50. If you value it a lot (and it seems that you do) you may want to invest in a real frame. I'm estimating your pennant is worth $250 - $300, so a nice custom frame job could easily cost you the same as what the pennant is worth.
Here's a final option available on ebay... a nice pennant frame but not fancy. Still rather expensive at $100....
http://cgi.ebay.com/WINNING-STREAK-C...item5d2c4f8e83