Eric Clapton joins in next for a bluesy rendition of Nelson's self-descriptive standard "Night Life," and while Slowhand's stinging electric guitar work takes the song places it has never before gone, his vocals are ragged and thin and Nelson's are desultory at best.

Perhaps it was just an off-night for Willie's next guest Shania Twain, or perhaps her skittish, wavering performance on "Blues Eyes Crying In the Rain" reveals just how much help her producer-husband Mutt Lange provides in the studio. Nonetheless, despite Nelson's best efforts on harmony vocals and his signature guitar picking, one of his most iconic songs (originally on his breakthrough "Red Headed Stranger" album), sadly, does not fare well at all.

Things pick up greatly with a jolt both musical and conceptual: a live version of Nelson and Toby Keith's number one smash "Beer For My Horses." On the musical front, the band finally has something to sink its teeth into, which it does with relieved vigor, and Keith's hale baritone is a great foil for Nelson on this anthem that both celebrates and pokes good-natured fun at core country symbolism. You have got to love a song with a chorus of:

"We raise up our glasses against evil forces,
Singin', whiskey for my men,
Beer for my horses"

Besides being the centerpiece of this set, the tune is also up for the Best Country Song award, an award songwriters Keith and Scotty Emerick are likely to win against Twain's "Forever and For Always," Brad Paisley's "Celebrity," Alan Jackson and Jimmy Buffett's "It's Five O' Clock Somewhere," and Pat Green's "Wave On Wave."

Not only is "Horses" an instant classic musically, but it also brings together country's absolute political bookends: Keith, the Dixie Chick baiting pro-war patriot, and the iconoclastic, pot-smoking lefty Nelson, whose quixotic endorsement of Dennis Kucinich for president and release of the anti-war, anti-Bush song "Whatever Happened to Peace On Earth?" puts him squarely at odds politically and culturally with both Keith and the mainstream country music audience. If Keith can get this cozy with Nelson — and why shouldn't he? — one wonders why he hates the Dixie Chicks so much.

There are nice moments the rest of the way, even if it ultimately doesn't all add up: Diana Krall and Elvis Costello on Nelson's most famous composition, "Crazy," a preposterously great rasta version of "To All the Girls I've Loved Before" with Wyclef Jean, and the sublime Norah Jones on "Wurlizter Prize." The record is good but it could have been much more.

Though this album could well win the Grammy on strength of its "event" status, Willie's duet with Ray Price, Run that By Me One More Tme, is actually a better album.