Impersonate vs RunAs user

[Boni]

I have to send some epl's commands to a shared printer. I would an asp.net
service doing this from my web server to a pc client wich has the shared
printer plugged.

If I exec my application like a console application it works, so like
running the service inside a cassini web server. Using IIS it doesn't work.
Off course in the first two cases the applications running with
administator's privileges so I tried to using the "Impersonate" script in
order to exec the commands with more higher privileges .
Despite this using the server's administrator account under IIS the service
doesn't work but if I use a domain's user account it works. ( the server is
outside the domain ).

I don't understand the difference executing code between using the
Impersonate or as a normal program.

Thnak's for your help.