You need to use AND instead of OR
SELECT
tblcomputers.ComputerUnique,
tblPrinters.Caption,
tblPrinters.Portname,
tblPrinters.Sharename,
tblPrinters.Location,
tblPrinters.Comment
FROM
tblcomputers
INNER JOIN tblPrinters ON (tblcomputers.Computername = tblPrinters.Computername)
WHERE
tblPrinters.Caption NOT LIKE 'Microsoft%' AND
tblPrinters.Caption NOT LIKE 'CutePDF%' AND
tblPrinters.Caption NOT LIKE 'FAX' AND
tblPrinters.Caption NOT LIKE 'Adobe%'