WOW! If they get Hirsh, Taveras and Buchholz you gotta think thats a good deal. Hirsh is a real good prospect, Taveras gets a lot of steals and is a solid defender, I believe. Garland is vastly overrated, his BAA was almost .300 in 2006, he doesn't get a lot of strikeouts, and for his whole career he's been a mediocre pitcher, 4.5 ERA and 12 wins or so, except for 2005. The bloated win total in 2006 was mainly because of the Sox' offense.
That said, if I were Ken Williams I would have traded Garcia or Garland, not both of them. But their future looks pretty good with Floyd, Gonzalez, Hirsh, Taveras and Buchholz into the mix, and a secure spot in the rotation for McCarthy.
EDIT: Another thing that could be going on is Williams sees the likes of the Twins, Guardians and Tigers and realizes he will be competing with them year in and year out in a tough 4 team race. Maybe he is looking towards the future more because those teams have a lot of good young talent, and the White Sox, without these trades, could not compete with them in later years.