ok so you wanna aftermarket HU. First choose which HU ur after. Then take ur old HU out and it shud have a cage around it, remove that or u can buy a new one for about 99p and thats that. To remove the old HU u will need to undo the 2 screws underneat the ashtrau on the panel and there is also 2 screws elsewhere...cant think of top of my head someone will know. Anyway, then you can remove the centre panel thing and easy access to your Hu.
There is a wiring loom that comes out of the HU and joins into another loom. When you buy an aftermarket HU, the loom on the back of the Hu will not fit into the other loom so you need to buy an ISO adapter lead (usually on ebay for like £2) but can get from anywhere like halfords n motor-world. ( I think the one ur after is for all nissan models ) If in doubt ask, the bloke will know what ur on bout. Anyways, this adapter goes in between the loom from the Hu to the other one so joining them. Dont attempt chopping wires if u dont know what ur doing. Then simply screw the dash back in and bobs ur uncle. Oh yeah, u might need an arial adpater thing, there about 99p - again the bloke will know what ur on bout, this just allows you to connect ur arial lead to your new HU.
I think thats all, you wont need brackets our out though
This is what your looking for:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=15329&item=7951033648&rd=1&ssPageName=WDVW
or any of the following at a quick glance
http://search.ebay.co.uk/nissan-ISO_W0QQfromZR40QQsojsZ1
