A very basic script would be this:
SELECT TOP 100 PERCENT
tblComputers.Computername,
tblComputers.Lastseen,
tblComputers.Username
FROM
tblComputers
WHERE
tblComputers.Lastseen < '10/05/08'
Of course the problem is that it has a date in it that would have to be changed each time it was run. I know little more SQL than a wombat, but it is a start.
You may find that the SQL builder isn't that bad once you get used to it.
Also if you want to save the report you need to have the top line "SELECT TOP 100 PERCENT ". The report builder puts in only "SELECT" so that took me a while to figure out as well. Another tip is if you have more than one table, you need to link them. You drag the Computername from one table to Computername in the other. Report builder will then make a line. This lets the SQL script know how to merge.
Best of luck.