Check your welcome email for what nameservers you will need to enter. If you need them again, please open up a support ticket so we can get them to you.
In order to change the nameservers for your domain please login to your account, go to Manage Domains and choose the domain you would like to edit. Click on Transfer DNS to Webhost (or Domain Name Server Setup) to setup the nameservers for your domain.
SOURCE : http://namecheap.simplekb.com/kb.show?show=article&articleid=285&categoryid=10