While rules and regulations vary between governments and airlines, and TSA policy is slightly ambiguous with respect to desktop computers, I have a suggestion that that may cost about the same as air cargo, but will provide a bit more peace of mind.

Assuming there's someone in the country you're going to that you can trust, give some thought to shipping it via UPS or FedEx. Address it yourself "in care of" the name of the person you're sending it to.

The biggest advantage(s) to this method, is that you can track the progress of your "shipment" on the website of the company in question.