connect to home PC from office PC located behind firewall and proxy

[mgp77]

I am very novice user of VNC and I am trying to
connect my VNC viewer at work (behind firewall that asks for a
http proxy account username an password which I don't know)
to my VNC server at home that is on the internet with
nothing restricting
access to that particular computer.

Now, if I dial in through my ISP and than try to
connect to the VNC server it works with no problems.
But once I am behind my office network firewall I
cannot get through
the firewall/http proxy with VNC viewer (because I do
not know how to configure
the viewer to access that proxy).

So in summary how do I get this VNC viewer to connect
through my firewall to my home computer
on the internet running VNC server.

I should mention that I do not have an adminstrative
privalleges to my office network. So
therefore I cannot make any changes to that.
Hope someone can help

Thanks