Cropping in photoshop

I have photoshop 9. something?

It is the latest version with all the add ons...


So, my problem is that, I dont quite know how to crop something to make the image smaller, yet keep detail.


This picture



Is what I want smaller.

I want it to be a bit smaller then thumbnail size as it is going to be part of my opening header on my site.

But, when I crop, or resize the image, I lose detail, or it only changes the size of PART of the picture..

And for the life of me , I can not figure out WHY or WHAT i am doing wrong.