Don't ever get a Samsung TV.
It really depends on the size of the upgrade, Minimum. If you're going big big, you should definitely run with an HDTV.
Cost is another factor. Headband has a point with most LCD HDTVs being 1366x768, and they don't really render text very well at that resolution. But many companies are putting out 1080p LCD TVs now, and they look really good. Costly though.
You're looking at $1,000 for a decent 26" LCD TV that's 1366x768 and won't really look great as a computer monitor (games look just fine, but desktop isn't real sharp). So if you haven't got a budget for more, you should probably just go with a monitor upgrade.