webservice proxy credentials

Question

hi,
I have some code that accesses an external website via a proxy.  This all works nicely when i am logged on as an admin.  However,  i have a windows service that uses the same code to do the same thing, and it errors with the log message  "unable to connect to remote server".  Essentially it is getting denied by the proxy.
If i go to the service and go to Properties, and then set the "Log On" option to use the admin account i log on with,  it works fine.  So i figured i just need to set the credentials of the proxy object in code to authenticate with the proxy server.  To test i just entered the admin account details i use (when it works fine).  This doesn't work.
It seems that nomatter what i put in the credentials, it just uses the details of who is logged on (or who the service is logged on as).  Even if i log on as the admin account and put junk in the credentials , it still works!   It seems to be completely bypassing the credentials.
Any pointers would be great!    (i believe it is something to do with the proxy server settings??  i have the same environment set up at home with FreeProxy and it works fine)
regards,