To be able to buy the house in Windhelm, Hjerim, you must complete the quest "Blood on Ice". You should then be able to buy the house for 15,000 gold (not including the upgrades). If all the upgrades are bought, it is a very nice house with three manicans to do the armor duplication glitch and everything else a house needs. It even comes with the room behind the false back panel you find in the quest, which contains an alchemy and enchanting station. It's almost as nice as the house in Solitude.
Edited: Jul 9 2012
Added by: MNvikingsfan1 Jun 6th 2012, ID#8435