Hmm best case scenario is that you probably only need to do some maintenance by removing excess dust on the laptop, but the fan error is rather odd so I highly doubt that's the case. Though what could have happened is your fan probably fried out and needs to be replaced; which will require you to purchase a new fan, and of course open up that puppy to replace it. The worst case scenario is that the fan connectors on the mobo for your laptop fried out and well you'll need one of those pad-cooler thingies...though I highly doubt this to be the case, but stranger things have happened so *shrugs*
The best thing I can think of for you to do right now is to try and remove excess dust around the vent holes of your laptop. Use a high powered vacuum with one of those attachment things that let you form a seal over things. Not really recommended, but its really the best way to get to the dust sans opening up your laptop. If the problem persists, well you may wanna take it to your buddy
Heh now I feel like a douche for always charging people for puter repairs
Oh right take a look at the bios/setup screen that appears during post (typically f10 or del or one of those buttons depending on the mobo) and try to see if you can access the page that details the current fan rpm's. Since you are getting a fan error post boot (already on the OS right?) that should mean that the fan is being monitored (should be able to disable this option at your own risk of course) and is shutting down your system since its spinning slower or something. If it's at 0 then that means its bork. If it's still spinning then you are golden; though you may want to do some dust upkeep anyway.
k now i'm just ranting so just update me when you get around to doing this.