If it's Thursday, this must be the mailbag . . . Q: I have a question I hope you can answer for me. Neil Patrick Harris appeared in a very short-lived series a short time before ''How I Met Your Mother.'' He played the part of a literary agent to a guy who put me in mind of Tony Shalhoub. This writer was funny and unique and had an assistant who was also funny. Can you tell me the name of the series and also the name of the guy who played the author?