9:30am: The AP is confirming the Rockies have signed Giambi.
Saturday 8:01pm: Tracy Ringolsby of Inside The Rockies says that "Giambi is ready to join Triple-A Colorado Springs where he will be given regular at-bats with the idea of being activated by the Rockies when the active rosters expand to 40 players on Sept. 1." He also mentions that the Rockies made a run at Tony Clark earlier in the year, but he balked at the idea of spending time in Triple-A.
6:10pm: Susan Slusser of The SF Chronicle hears that Jason Giambi is "getting close to signing with a contender to be add some bench power, and the team I'm hearing is Colorado." She mentions that the Rockies' interest is unconfirmed. Giambi was released by the Athletics earlier this month while he was on the disabled list, hitting just .193-.332-.364 in 83 games. I would think it's safe to assume he's healthy if teams are interested in signing him.
Not that the sample size is substantial, but Giambi is a career .283-.356-.509 hitter in 59 career plate appearances off the bench. Any team that signs him will only be responsible for the pro-rated minimum.