Bad news I am afraid.
Apple properly implement UAC (User Access Control) whereby whenever something tries to install itself it does ask for an admin level authentication. Microsoft's effort in this area ***** big time even if in other areas they may be better than Apple.
Therefore as things stand you need it to be authenticated by an admin level password.
Now looking forwards there are two possible approaches which would make both your IT department happy and let you work.
- If your IT department sets up a system whereby they can remotely control your computer they can remotely authorise the installation. This is an absolute pig to do with Windows machines as in Windows normally the authorisation dialog kills the remote control session but thankfully it is easy with Macs. This may require having a VPN connection to the office but some remote control systems do not need this e.g. LogMeIn
- or they could set up a 'self-service' software install system like Munki. There would be a server with the installers on it including the XCode installer and your Mac would be configured to talk to this, you Mac would have the Munki Managed Software client on it and this client would manage installing the applications and would also manage the authorisation for you meaning you would not need to enter a password
Even once you have XCode installed it is my experience that using it to develop software usually requires admin access anyway, the development company I worked at in support therefore conceded the inevitable and gave all the devs admin level accounts with the understanding that if they broke things they had to fix it themselves. 🙂