Yes, you can.  There are three ways to do this:

1. We can forward your incoming emails to your gmail mailbox.  They arrive within seconds, but when you reply the reply will come from your gmail address not your hosted domain address.  We can do this for hotmail, yahoo, or any other email service.
2. You can get gmail to fetch the messages from your hosted POP3 mailbox using the mail fetcher function in gmail.  You can set gmail up to reply from your hosted account as well using this system.  You do not need to contact us to do this – simply follow the instructions for setting up the gmail fetcher.
3. You can move your domain to google apps.  This means that we no longer control your email traffic and any new accounts or forwarders must be setup through google apps.  But this can be a very elegant solution.  To do this, setup your google apps account first, then contact support to send the MX traffic to gmail.