You're going to have to identify which row have the bad values and update them (or you can just update the entire table and set the column say to 0, but then you lose whatever meaning that column had)
The article I referenced has a link to a kb article that explains how to identify the rows with the bad values.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability