Dear Rich #2: I have a website that offers custom in-home computer services -- I'm like a geek squad business -- but so far, only in one state. If I register my trademark can I say it is used in interstate commerce? I'm so glad you asked. Short answer: "Yes, you are both in commerce." The fact that you are regularly entering into contracts (doing business) across state lines should qualify your trademark as being "in commerce" for purposes of federal registration. The same is likely true for a website offering services in one state since, according to one court, "the services are available to a national audience who must use interstate telephone lines to access the site." By the way, the "use in commerce" requirement refers to "all commerce which may lawfully be regulated by Congress," not just interstate commerce. So, for example, since the federal government regulates television transmissions, a TV station that broadcasts in only one state could qualify for registration.
The Dear Rich staff can't say positutely, whether performing services on an American Indian reservation constitutes commerce regulated by Congress (we think it does; readers, any comments?). BTW, you can find lots of other helpful free trademark information in Nolo's Online Guide to Trademark Applications (download it here).