From a wireless networking perspective I am happy to help here but please read on. The antenna idea is feasable if you have an external antenna connector on your laptop, if not you might need to consider a PCMCIA or USB adapter that does have such a connector. You will also need good low-loss cable if you intend to run more than a couple of metres. Such cable can be quite thick in diameter and is also quite costly.
More importantly though, as having many years experience as an IT administrator, I know that this type of activity is often very frowned apon not so much for personal use of company equipment but more from a network security point of view.
It is considered
extremely bad practice to connect personal computers to a company network as the contents of the computer are unknown and often unable to be monitored by network staff. The network becomes vulnerable to any malicious content that may be on the laptop (not necessarily deliberate). Good network administrators should have measures to help prevent this (network port authentication, intrusion detection, PKI, good monitoring etc).
If you are part of the IT crowd then you may already be aware of all this. This is all just my opinion so don't take it personally, I am just trying to help make you aware of the issues involved.