Your workplace has blocked your access to Gmail. Perhaps this is cause for finding a new job, but there may be a way around it so you can get your gmail messages. Try these resources for a start.
Access the Internet from a workstation.
Go to hideu.net or sneakyuser.com.
Enter the URL you want to access in the space provided on one of these sites.
Click away and hopefully you can access the blocked website through the anonymous user site.
Resort to a different mode to check your email if these anonymous user sites are also blocked.
Check your gmail via your home computer using a remote desktop connection.
Bring your own laptop and accessories to link to your personal email.
Consider using your cell phone or Blackberry to access your gmail if there's no way around having it blocked.
Confront the problem directly and try to get your office to change its policy regarding blocked gmail from your workstation.
If you use a remote desktop connection at work, it's probably best to run this by your IT department.
If your company has a strict policy against accessing personal email at work, you risk losing your job if you access email secretly from your workstation. Consider the risk before you click!