I'm using an ATI All in Wonder 128 PCI as my primary (and if you want the multimedia functions to work, it has to be set as your primary in your bios setup) card in a triple monitor setup. Good card and I've found the tv out function was easy to setup and to work very well.
That being said, Sony Vega or not I believe your resolution to tv monitor will never be as crisp and clear as your computer monitor for everyday apps but works great for playing DVDs, DivX etc to a larger screen.
Be careful if you display desktop or other static image to tv, I've heard that a tv is much more sensitive and displaying static images over a long period will burn a ghosted image to the inside of the screen.
Are you planning to go multi monitor (or maybe you allready are multimonitoring), just curious as I've been running this setup for two years now and could give you some advise of what to avoid. If you are planning to multimonitor with just the one ATI All in Wonder 128 PCI card and tv out, don't expect to extend your desktop to the tv and be able to work on your monitor the same time as you are playing a DVD for the family (with the ATI All in Wonder 128 PCI, tv out will play exactly what your primary vid card is processing) To do this you have to go to a multimonitor setup.
Have fun, I know I always do.