Roundcube is a standard webmail "client" (basically means email program) that we offer to Afrihost Clients with their hosting. To use Outlook Express, you will need to switch from using an online web based mail client to one hosted on your local PC.
Via cPanel, we do have custom scripts which can do the mail client configuration for you, but it will depend on which version of Outlook Express you are using and if your system is compatible.
Otherwise you will need to manually create and configure your mailbox on your PC, using the Mailbox Wizard and the settings provided when you signed up (i.e. username, password, incoming and outgoing mail). These settings will vary according to your requirements, but usually we use mail.yourdomain.co.za on port 110 for incoming mail and smtp.afrihost.co.za on port 25 (if you are on Afrihost broadband) for outgoing mail. You will need to ensure that outgoing authentication is switched off.
Here is a step by step process on Outlook, which is very similar to Outlook Express.