When submitting this Querey in SQL Server 2005
SELECT FT_TBL.Firstname, FT_TBL.LastName, Key_TBL.Rank
FROM [user] AS FT_TBL INNER JOIN
  CONTAINSTABLE([user], Firstname, 'ISABOUT (Christian weight (.1), Ian
weight (.2))') AS KEY_TBL
  ON FT_TBL.userid = KEY_TBL.[KEY]

I get this message:
Msg 7607, Level 17, State 1, Line 2
Search on full-text catalog 'ft' for database ID 9, table or indexed view ID
789577851 with search condition 'ISABOUT (Christian weight (.1), Ian weight
(.2))' failed with unknown result (0x80020005).

The only way I can run the querey succesfully is if I change the weights to
either 0 or 1.

@@Version returns this result for your information:
Microsoft SQL Server 2005 - 9.00.1399.06 (Intel X86)   Oct 14 2005 00:33:37  
Copyright (c) 1988-2005 Microsoft Corporation  Enterprise Edition on Windows
NT 5.2 (Build 3790: Service Pack 1)