Assuming you have the iso file downloaded onto the netbook, you might wish to keep the Windows 7 system it has already for the time being, in case Windows 8 is unworkable.
Because of screen resolution, Metro does not work well on netbooks.
You either need a USB external disk - a hard disk or reasonably fast Thumbdrive of greater than 16GB - a 16GB SanDisk Cruzer blade is workable - OR you need to make a partition on your hard drive of size greater than 20 GB.
Do this from Windows 7 on the netbook:
Assuming partitioning is needed, search diskmgmt.msc to open the disk management console
I don't know how your ASUS is set up, but there will probably be a hidden recovery partition of about 13 GB, an System Reserved partition of about 100MB, and a main Windows 7 boot partition filling the remainder of the 320GB disk.
If it is like this you need to shrink the main partition - select it, and right click and shrink volume - you need to shrink space by about 24000MB to give a working size for Windows 8 - create an extended partition and a logical partition within that for your new installation. This needs to be formatted to NTFS and given a drive letter.
ISO files are not mounted natively by Windows 7 - you may need to get something like Elby CloneDrive
elby Free Software to enable you to mount the Windows 8 Install iso on the netbook as a BD_ROM drive.
Once Mounted, the important file is in the \sources folder called install.wim
The following is done from an elevated command prompt
For this example the BD_ROM Drive letter is d: and the Drive you plan to install windows 8 on is T:
dism /apply-image /imagefile:d:\sources\install.wim /index:1 /applydir:T:\
On a hard disk the time is about 20 minutes, on a thumbdrive, over an hour is normal.
Once the application reaches 100% successfully and returns to the command prompt, type
bcdboot T:\Windows /s c:
This adds an entry to the Windows 7 boot manager to dual boot to windows 8 - text mode boot menu - best not to change to the Windows 8 boot manager yet.