Another +1 for LogMeIn. The initial install is the only slight hurdle but it's not hugely complicated - best thing is for you to register for the account, then I think you'll need to give him the email address/password so when he installs the client application it gets linked to the right LogMeIn account.
Once installed you just visit their website, log in, and the computer should be listed and it will tell you whether it's online or offline. If online you can connect straight from the browser (you'll need to know the username/password for a local account on his computer though).
Also I'd recommend you use Firefox for this, as there is a decent plugin which you'll be prompted to download from the LogMeIn website which makes the remote control experience much nicer - Chrome and IE just rely on Java and IMO it's slower and the picture quality is much worse.