I'm using boto to spawn a new EC2 instance based on an AMI.
The ami.run method has a number of parameters, but none for "name" - maybe it's called something different?
In EC2 there's no api to change the actually name of the machine. You basically have two options.

You can pass the desired name of the computer in the user-data and when the server starts run a script that will change the name of the computer.
You can use an EC2 tag to name the server ec2-create-tags <instance-id> --tag:Name=<computer name>. Downside to this solution is the server wont actually update to this name. This tag is strictly for you or for when you're querying the list of servers in aws.

Generally speaking if you're at the point where you want your server to configure itself when starting up I've found that renaming your computer in EC2 just causes more trouble than it's worth. I suggest not using them if you don't have to. Using the tags or elb instances is the better way to go.
With boto, how can I name a newly spawned EC2 instance?