I worked at a law schoool for a little while fixing students laptops. Law school students have rich parents, which means they have very nice very expensive laptops. I saw some really sick ones, ones that cost 3 or 4 grand. I saw one with a 6600gt! LAPTOP!!! Insanity. But I also saw a few kids who had theirs stolen. Sucky, since the school is totally not liable. You are SOL if it gets stolen. Remember to get one of those cable locks. They wont stop a theif, but they do deter them.
I would totally go with the good desktop/cheap laptop. Go to a little local computer repair shop, and get an old used one for your work, like Chankama said. Get a crappy one for a few hundred dollars (hell, even check Ebay) and throw some money into a custom desktop. Desktops are better for gaming anyway, as you can get in them and upgrade them and the such. Plus, you can build one from scratch without spending a few thousand.