Create a new table in lansweeperdb called ExcludedMachines, with a single column to hold the Computername ID.
CREATE TABLE lansweeperdb.dbo.ExcludedMachines (Computername INT PRIMARY KEY);
Add the Computername ID of the machines which you want to exclude to the table.
You can now add a WHERE ... IN check to the reports in question. For example, for the web40repHDDFreeWorkstations (Workstations with less then 1GB free), add the following to the end of the WHERE clause:
AND lansweeperdb.dbo.tblComputers.Computername NOT IN (SELECT Computername FROM lansweeperdb.dbo.ExcludedMachines)
This will allow you to add machines to the excluded list without having to change every report in question.