Technically, you CAN clone from a larger drive --> smaller drive. But considering that you've already used 150GB, it will be a big pain to deal with that... on top of the typical problems of cloning larger --> smaller drives (such as corrupted boot info that needs to get repaired).
Best bet is to just do a clean re-install of Windows onto the SSD for several reasons:
(1) Windows will automatically configure itself to use an SSD during the install process (turn off defrag, turn on TRIM).
(2) This is a good opportunity to "clean" your Windows installation by getting rid of all of that junk (and registry bloat over time) that you don't need anymore.
(3) You get to watch how fast Windows installs on your new SSD. There really is no better way to play with a new toy than to reinstall Windows onto it, and be amazed at how fast it goes.
