Centos 5.5 seems to be out of date (linux moves much faster than win), but you really need to speak to your company's IT department, and ask them:
How have they set up their VPN?
How do they suggest you access it?
If you have linux-specific problems ("I tried this .... The error message was ....") we are here to help, but I think you need to make the first move with your company's IT department.
Welcome to LQ!