You phone MS up, they log it as RROD and replace it free (because it's a common problem and easily fixed). Either they send you the details to print off and attach to the console packaging, or you go to their website and do it yourself. Sort out the DHL courier or whoever they're using now (or they'll do it themselves - I forget which). You pack it all up for them, DHL come out and take it from you, send it to Germany, it gets repaired and sent back to you. Job done.
They usually sort the fan and laser out, but when mine RROD'd, I just went out and bought an Elite the very same day. I'm impatient like that. Sent the duff one away, got it back within 7 days and sold it to a guy from work for £100. It actually looked like a brand new console they'd sent me (definitely had a new disc drive, as it was still sealed).