For that wallpaper goto
here.
To change a bucket load of settings, without installing 3rd party software, you can simply use windows
Here's how to change
Icon Size:
Start
Right click on your Desktop and select
Properties.
1
Click on the
Appearence Tab.
2
Click on
Advanced (you can tell this stuff is hard

), this opens a new window.
3
Under the
Item Dropdown list, select
Icon, to the right of that is a Pixel Size box, type in a number, noting that your icons can have to support 'BIG' otherwise they will look all pixelated, and whilst I haven't tested this, I believe windows only lets you take it up to around 72.
You may also want to change
Icon Spacing in the horizontal / vertical controls from the same dropdown list, otherwise you can end up with nasty spacing (which only takes effect with a reboot

)