Check the tightness of the power steering pump drive belt, it may be slipping and causing the squeaking noise. Check the steering fluid level. Check for fluid leaks from the pump to rack hoses. Check that the rack boots aren't torn or split. Check the condition of all steering linkages and check that nothing is binding when the steering wheel is turned lock to lock. Does the problem go away if you jack the front wheels off the ground and turn the steering wheel? If the fluid has been run low you may need to bleed the steering system.
I don't have a manual for your truck but I think the bleeding precedure for bleeding the power steering flluid out lined in the 2003 Tacoma shop manual should work on any vehicle. See;
http://fsm.afraid.org/
Click on volume II and find page SR-4 in the Steering system.
If you find nothing externally wrong the steering rack probably has an internal problem.
Clifton