Same here my northbridge is hot to touch even though I never overclock, however this is fine with suficient cooling; as you can see my case has plenty of cooling however yours as you say only has 1 80mm intake. It is also god that you have a slightly negative pressure in this case as this keeps the hot air out (2x 120 mm outake +1 80 mm intake= slightly negative air pressure within the case (this is good)).
I see your northbridge is tilted this may cause problems if you have a low seated heatsink on the cpu so I reccommend before you buy a northbridge heatsink to check that the heatsink will fit on your mobo. The details of hight width etc are usually listed with the product however if not go over to the manufacturers website.
One very good one that I would recommend is this one provided you live in the UK dont know if its available in the USA:http://www.dvhardwar...techMCX159.html
Note: This is only the review site where full details of the hight etc of the heatsink + fan is available as well as of course the review. Also note to get the Intel version if you do get this.
To remove the original nothbridge heatsink you will have to remove the motherboard well I have to on mine and yours looks very similar........ does it have white push pins with springs which do not come out if you push them down? If yes then yes you will have to remove the mobo.
The process of applying a heatsink is generally the same for GPU, CPU etc, I recommend using High purity isopropyl alcohol, and some cotton buds or lint free cloths. Dip the cotton bud in the alcol and clean off the excess old thermal paste off the northbridge chipset once the old heatsink is removed.
it should not be dripping only soaked in alchol. Now make sure you do not drip any outside of the chip itself as you may damage something.
Next follow the instructions supplied with the northbridge cooler.
The one you show is ok but I generally dont like thermaltake cooling even though their cases are nice! Zalman is one very good company.
Tell me if you need any more info.