Dell is a big fan of proprietary computer parts, so I'd suggest looking at http://support.dell.com and search the user support forums for your fan error message and model number to double check. If the heatsink aka cpu fan is proprietary, at that age, try ebay for replacement fans/heatsink. Depending what that model uses, you may be able to just swap out the actual fan even.

If its not proprietary any fan that fits the motherboard will work. They can be had for about $30, if its the actual heatsink.

Dell has excellent information on their support site about removing and replacing most parts. Atleast with the XPS I had. Tells you what all to take out to reach most things.