How guys I plan on building a 350, and using nitrous with it. Some one told me that i need to usiing a nitrous cam and not a mild aftermarket cam. Can anyone help explain why this is so??

Unless your building a nitrous drag motor don't worry about it. For a 150 shot or less street car just run a good cam with your motor.

How much and how often?

100 shot and mainly on the weekends at the track.

nitrous cam usually means large separations for valve events so that there is less overlap. this helps nitrous stay in the cylinder, and it causes the engine to rely less on exhaust gas velocity and port size to determine the overall filling capability.

basically, you are injecting the oxygen, so why worry about maximizing VE? We will just simulate our VE with the nitrous.

Stick to a regular camshaft so that off-nitrous performance does not suffer.
And if using something with a healthy overlap, size the exhaust plumbing to mate the manifolds (all of them) and head port sizing so you dont want up with poor velocities that leads to intake charge contamination and loss of VE.