Every game jam needs a place or a method for the participants to sign up. For the Global Game Jam, there are two ways to do this:
1.Use the sign-up for the global game jam.
2.Use your own sign-up forms at your local game jam site.

Using the Global Game Jam sign-up

The Global Game Jam sign-up is set-up so that an email is automatically sent to a local email address of your choosing, whenever someone signs up for your specific site. (Note: The global game jam site does currently NOT send emails when users sign up.)
For each person that signs up, you need to send out an email to that person giving instructions on payment, location, what to bring, etc.
Depending on the number of people you expect for your jam, you will probably want handle this in one of two ways.
1.Have a person check through the sign-up emails on a regular basis and send out the necessary emails manually.
2.Have a small webservice that wakes up regularly to check the email account used for sign-ups. This webservice will read the sign-up data from the email, put that data into a database for later use, and automatically create and send out the necessary confirmation email with a thank you and payment and contact information.

The first method has the advantage that it takes less work up front, and there is no need for a running database or even a website. The second method does need some programming up-front as well as access to a database and a server where you can install a daemon. However, it will save a lot of work later on, you will have a central place where participants are organized, and registrants will get a near immediate confirmation on their sign-up.

Your own sign-up form

For the Nordic Game Jam, we have our own sign-up. The reason is that it gives a more local feel, and that we can customize the sign-up form to fit with our local needs.
For the technical solution we use a simple custom webservice created with php and mysql. This solution also has the advantage that it is easier to set up, than the technical solution described above, where you have to do email parsing as well as having a local daemon that wakes up periodically. Most hosting services offer a simple php and mysql solution, while the latter can be harder to find for a reasonable price.

Experiences from NGJ

We have always had an online registration form for the Nordic Game Jam.
This has really helped us a lot, as confirmation emails are sent out automatically. It is also very easy to extract emails from the database for the purpose of sending out reminders and thank you notes.
During the sign-up, our participants fill out forms telling us which software they prefer, if they have a group, etc. We use this information to get an idea about logistics before the event.

The sign up forms for the Nordic Game Jam 2008 is still online and can be found at here. The automatic sign up procedure also makes sure that everyone can at any time check out the current list of participants.

Checklist

Have you thought about:
1.Even if you choose the solution of manually reading through sign up mails, it might be advantageous to enter participants into a central database. This will help later, when you want to send out bulk emails for confirmation, thank you's for participating, reminders, etc. It will also help when extracting information and statistics from the forms.
2.That if you create a webservice, you really need volunteers for testing it for you before it goes live.
3.Confirmation emails need to have payment information as well as contact information for your local game jam.