>is something like this possible? I get an error, but I thought it should have worked:
>

>UPDATE EmpItems 
>    LEFT JOIN HistItems ON HistItems.eiKey = EmpItems.eiKey
>    WHERE HistItems.DelFlag = 0 
>    SET EmpItems.itOnPosted = 1, EmpItems.itBalAmt = HistItems.itBalNew + HistItems.itPostCalc
>

>Maybe I'm doing something wrong?

You are missing FROM clause. The syntax for UPDATE -SQL command is:

UPDATE Target
SET Column_Name1 = eExpression1 [, Column_Name2 = eExpression2 ...]
[FROM [FORCE] Table_List_Item [[, ...] | [JOIN [ Table_List_Item]]]
WHERE FilterCondition1 [AND | OR FilterCondition2 ...]