monitors and threads

i have 2 threads both of which read and write to an arraylist,

does c# have anything built in that does this?? or would i have to write my own??

i also found the Synchronized method of arraylist which returns a thread safe wrapper, but, when i read further it says its not thread safe if u Enumerat it, but would this just be when using the Enumerating method or would the genraly apply if one thread was going throguth the array and the other modified it??

how would it deal with one thread modifying it at the same time another was accessing it??