Is power steering flush necessary - 2001 Nissan Altima

No, that is dangerous for you, as the steering will become very very hard, too much for good control. In an emergency fill it with water or thin cooking oil if absolutely necessary, then have it flushed out ASAP.
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Here's a video on flushing your power steering. How to Flush Your Power Steering Fluid

You need to buy a Haynes manual for that car and will help the do it yourself repair and flush system k

hope this one help http://www.popularmechanics.com/cars/how-to/maintenance/3322636
This instructable is designed into four main parts. Here's the outline:

1) Gather the materials
-- Instructable step 1 - This includes tools, a new pump, fluids, etc.
2) Remove the leaking pump
-- Instructable step 2 - Drain the Power Steering system
-- Instructable step 3 - Remove accessories from Power Steering system
-- Instructable step 4 - Remove the pulley and bolts
-- Instructable step 5 - Remove power steering pump
3) Install the new pump
-- Instructable step 6 - Place the new power steering pump
-- Instructable step 7 - Press on the power steering pump pulley
-- Instructable step 8 - Align the pulley and attach the belts
-- Instructable step 9 - Flush and fill the power steering system
4) Cleanup
-- Instructable step 10 - Cleanup

You'll need some tools to complete this task. Before you start, gather the necessary equipment -- you will not be able to use the car once you start the replacement! It is always a good idea to have a friend on call, or a second car available.

Equipment list:

• Power Steering pump (to replace defective pump)
• Two (2) quarts power steering fluid or appropriate ATF (to flush and fill). More than 2 quarts if flushing the rack is desired.
• Power Steering Pulley Puller set (to remove and attach the pulley). Some auto parts stores will loan the tool sets.
• Socket set.
• Open end wrench set (for use with puller set).
• Leverage pipe or extension bar (in case the pulley is hardened on the spindle).
• Drain pan (to drain & flush power steering system).
• Wheel bearing grease for sliding pulley on the pump hub.
• 2' wood 1x2 for assistance with aligning the pulleys. Any straight tool will work fine -- a level, metal rod, wood, whatever.

Check you fluid level and add some if necessary. If it looks dirty you might need to flush you power steering system. Lastly it might be that you ;power steering pump is going out.

it never hurts to service the power steering and the transmission, but at 70xxxmi it is not necessary if you check the owners manual it should show a transmission service at 100xxxmi but you will find nothing in the owners manual about the power steering this is a fairly new thing that we are seeing some shops do, i am not sold on weather it needs done at all.

its another way of printing money for any dealer...........same as buying accesories when buying a new car,they prey on your excitement of purchase.

I wouldn't flush the trans,just remove the pan.

You should change trans fluid, every couple years and not more than 30,000 miles, on all vehicles.

Some will disagree,but I used to own a trans shop. 90% of all that work,come from not changing fluid. Same on power steering fluid

You need to raise the vehicle so that the front tires are off the ground and place on jackstands. Make sure the power steering reservoir is full. With the engine off (not running) turn the steering wheel from stop to stop 2 or 3 times. Recheck the fluid level and add if necessary. Lower the vehicle to the ground. Start the engine and slowly turn from stop to stop 2 or 3 times. Recheck fluid level. If no groaning noise is heard when the engine is running or the steering wheel is turned, and no foam is observed in the reservoir when engine is stopped, then bleeding is complete.

Regarding the steering, check the tightness of the power steering belt and the steering fluid. Some places can flush the fluid if necessary. Check for leaks at the power steering lines and the inner tie-rod boots if the fluid is low. If the fluid is ok, no leaks and the belt is tight the pump may be going or the steering rack could be binding which means replacement of either if that's the case. If the pump groans loudly when turning that will indicate a problem. If the belt is squealing it may be too loose, worn or the pump pulley may be binding.
Good luck