Question

How do I take the information from 1 column/field in a table and add it to another field in a different table without overwriting what is in there?

Example:
From: Table 1
client.notes

To: Table 2
Add client.notes to the item.description (but not overwrite what is already in the item description field)

Answer 1

Something like this

UPDATE ITEM SET Description = Description + Notes
FROM ITEM
  JOIN Client on Client.Column = ITEM.column
WHERE Condition = TRUE

MSDN article on + String Concatenation
http://msdn.microsoft.com/en-us/library/ms177561.aspx

MSDN Article on SUBSTRING which you may find useful as well
http://msdn.microsoft.com/en-us/library/ms187748.aspx