basically, you're going to want to use a database for this. This isn't that hard to set up, and there are a number of good tutorials and docs online (i'm leaving that part up to you).
Here's the basic concept. You create one page that will hold the comic strip of the day. In your database, you'll have a table that will relate the day to the comic strip file (the actual .jpeg or .gif).
When a user requests a comic, your PHP script will query the database (this is easy... just find a quick tutorial) for the name of the file that belongs to the specific day.
There are a number of methods for linking between strips... if you reliable and consistantly release strips everyday, you can just make a "back" link that will go to the previous day. i.e) if you're looking at Jan 3, 2001, then the "back" link will go to Jan 2, 2001. Of course you'll need a little bit of logic to account for going from the first of one month to the last of the previous... but that shouldn't be a problem.
Another method would be to query the database for what the previous page should be, etc. Forward is more-or-less the same deal... obviously you'll have to stop at today (i.e. you can't view tomorrow's comic today).
You'll also probably want to make a page (for you, not the users) where you can add/remove/modify comics
Just read a few of the tutorials, set up a database, and you'll be rolling in no time. This is a great project to start with; it's relatively simple and it'll get you familiar with most of the basic concepts of PHP (databases, etc).
If you already program, you should be able to whip this out in no time. Otherwise, be patient, ask questions, and enjoy.
-Andy
