Assuming that you mean Windows 7, I recommend against what you are doing strongly.
If you want to put Win7 on an SSD, the consensus here is that you should do a clean install (search the forums if you don't believe me). The SSD should be attached to a controller in AHCI mode during installation, and an external enclosure will not provide AHCI mode.
Short form: Disconnect all current hard drives from PC (no need to remove them), attach the SSD internally, ensure (in the BIOS) that the SATA port is set to AHCI mode, not IDE, and do an install.
Long form: read our own Tecmo34's guide:
http://www.computing.net/howtos/show/solid-state-drive-ssd-tweaks-for-windows-7/552.html
I know that I didn't address your main question. That's because, unless you are doing the experiment for a very strong reason, you don't want to clone an existing Win7 install to a new SSD, let alone a new SSD in a USB enclosure. Among other problems, the drivers will be wrong.