If you ever overheated the motor, head/block must be milled.
If you're replacing w/a mls headgasket head/block should be milled though i have heard some people, not sentra owners, use a very fine grit sand paper on a small aluminum block and sanding down the surface lightly while spraying wd-40 to prep. Some use copper spray w/o milling the surfaces and just sanding. Can't say it won't leak but some found success.
If you never overheated and you plan to use just the oem composite gasket, you should be fine just to remove all previous gasket material w/a razor blade. I doubt milling is required.
Another tip, just as bigdave did, mark your chain/camgears/crankshaft w/a whiteout or something to make sure you're able to reinstall your chain properly. Once the chain is reinstalled, rotate the crank slowly by ratchet to confirm the valves and pistons clear. No need to disassemble your head unless you plan to change your valve seals too.
Good luck and keep us posted w/your progresss
Last edited by LowBudgetBaller; 02-04-2008 at 02:10 PM.