That doesn't mean its not a zombie network either. Or maybe even a bad link on a popular web site.
You haven't really provided enough information to convince anyone that something is wrong either. It's not exactly a bad thing if you get a strange request now and then. Requests come from other computers, not the server, and you may never know why the other computer decided to make the request given that there are no issues with DNS or virtual hosting.
At this time, if I were you I would check to see if the referer field in access.log appears to be valid enough to determine if it is a bad link causing the requests. Then I'd note the url-path make a script log any query or POST data to rule out exploit attacks. Then note the frequency (is it 100 times a second or 100 times an hour?) and contact support if the frequency is extremely high in case it is a DDOS. 200 hits a day is not a DDOS.
You might want to make a script that checks to see if the Host header being sent is your domain. The host header appears in the HTTP_HOST environment variable.
[color=#6600CC]Atropos[/color] | openvein.org