That text is part of the image: http://www.whitehouse.gov/assets//hero/hero_bkgd_united_we_serve.jpg
You can use a font service like WhatTheFont.com to find a closest match.
As for your second question, you can create a table the size of your background image, and use css to set the background of the table to that. Afterwards, just input the text in the table cell and use
style="text-align: center;"
to center the text.
You might want to use Photoshop to wipe the original text in background, as noted above.
It looks like Garamond. It is the same font used in this document:
http://www.hud.gov/united-we-serve/united-we-serve.pdf
It is distinguishable by the fact that the vertical lines inside of the W cross over each other.
In order to use the font successfully on your web page, it has to be installed on the computer of the user viewing it. Garamond is an Adobe font used on Apple Mac computers, and it's installed on my stock Windows XP computer, so I imagine almost everyone has it already.
Cufon may provide what you need to embed a non-system font in a HTML page: http://cufon.shoqolate.com/generate/
There are a few caveats when it comes to licensing, and a few browser issues, but it works fairly well for the most part - certainly better than sifr.