Yes, You can start uploading files to your websites even if your domain name has not registered yet.
Do the following to access the FTP without a domain name.
Enter this into your ftp manager: YOURUSERNAME@xxx.xxx.xxx.xxx Replacing 'YOURUSERNAME' with the user name from your control panel,
and 'xxx.xxx.xxx.xxx' with the server IP address. Both these can be found in your dualworkz welcome email you recieve after completing your order.
You can use the temporary URL which is provided in your welcome email if you wish to see your website without the domain name.