Saruman's acquiring of Isengard
 

In my Middle-Earth knowledge, I still do not know how Saruman came by Isengard. Did he ask for it, did the men present him with it because they thought it would do him more good then them, or did saruman use his voice to convince them to hand over the fortress? I might have missed something in the book, or a small description. They said he was given the keys to it by the steward or something like that(i'd quote it but my trilogy is loaned out to a relative) but I was always supsicious that Saruman used his voice as I dont think Gondor would have so easily handed it over to him. Does anyone have any info on this? Anything would be appreciated.

Here is a reference for you:

Isengard

You can also find it in 'The Tolkien Companion' by Tyler - p. 238-9.

There is also a reference in the Barrow Downs' Encyclopedia in the section on Saruman:

Saruman

Saruman settled in Isengard in 2726, after Rohan had suffered from invasions and Long Winter. Sone invaders,the Dunlendings came from Isengard. When they had been finally driven away by forces of Gondor, the Rohirrim were weakened and grieviously reduced.
Beren the Stuart was only happy to welcome a powerful friend at the border of the allied realm, which was rather helpless at the moment. The more so that Saruman was supposed to hold Isengard as Stewart's lieutenant.
I don't think that Saruman had to use any of his powers to convince the Stuart give him the key. At that time such an arrangement must have suited both (or better say all the three) sides involved.