I intend to offer some Microsoft Excel tools from a site whose name I'd like to be something like www.exceltools.com, I'm worried whether it will impinge Microsoft's trademark term.I know using any company name in the domain name is forbidden though (like microsoft).
Using excel word in the domain name
domains
You mean like excelhero.com? There are hundreds and quite frankly MS will not take action against you. In fact if you do write some good material and offer quality tools, they might even make you an MVP! 