I've successfully installed Windows 7 on my Eee Box (B202) without an external DVD drive, here is how:
1- Download Windows 7 (or get the iso file)
After logging in, save the CD(Product)-Key
2- Download and Install MagicDisk - Virtual CD/DVD Manger (freeware)
Maybe other virtual DVD tools will work also, but this one is for sure.
3- Mount Windows 7 iso and run it
Right-click on MagicIso's icon in taskbar -> Virtual CD/DVD-Rom -> X: No Media -> Mount
then locate Windows 7's iso file
the auto run will occur, otherwise manually run the setup file
4- Follow the Installation Instructions
Remember: don't overwrite the recovery partition
5- Install the Wireless Lan Device
After loading Windows 7 all hardware devices will work well except the wLan, so you have to install it from the drivers CD or asus's site