I have a server that does not have a CD/DVD drive..
How can opensolaris be installed using USB interface? specifically what tools/steps that need to be performed to prepare USB flash drive as install media?
If you're creating a live OpenSolaris USB disk from Windows, use the following program: http://devzone.sites.pid0.org/OpenSolaris/opensolaris-liveusb-creator
If you're creating one from a unix-y environment, this should do: http://chonan-en.blog.pid0.org/2009/11/how-to-create-opensolaris-live-usb.html
You should be able to install OpenSolaris from a live CD according to OpenSolaris documentation.
(Disclaimer: I'm not an OpenSolaris user, so I may have missed the mark somewhere.)
Maybe this blog post can be helpful for doing this: https://blogs.oracle.com/clayb/entry/creating_opensolaris_usb_sticks_is