Each player was a first-round selection in their respective drafts but neither of them have really panned out as successful major league players.
Kotsay was getting his playing time at first base, but he was optioned to the minors around the time the BoSox received LaRoche and Chris Duncan in deals.
Since then, he's been useless on the team. In a month-and-a-half of games, Kotsay has only hit one HR, five RBI, four runs, and stolen two bases.
I'm sure the mindset for Boston right now is to obtain decent backups for their stars while they make their run at the playoffs. Brian Anderson helps bolster their outfield with his stellar defense (five errors in 331 major league games).
As for the fantasy-side of things, neither are appealing in anything but the deepest of leagues.
Brian Anderson is a little more fantasy-relevant than Kotsay right now because if someone would get hurt in Boston, he would get some playing time in a loaded lineup.
Monitor both of them in the next week or so to see how they fit in with their teams but don't pick either up unless you are in desperation mode in a deep league.