IIS logfile rotation is pretty decent these days but archiving is, as far as I know still non-existent. IISFAQ has something in Article 141
but I think that's rather rudimentary.
My linux box already came with cron preset to take care of all this.
Today I wrote a rather crude batch file that looks at the date, gets the previous month from it and copies log files from that month. I needed that to get input to be processed by WebLog Expert but this could be easily modified to zip last month's logs and then delete the originals.
I need to polish the code a bit. When I'm done with it I'll post it here.
Won't be soon because next week I'll be on vacation.