Usually, when I need to copy a file from a Windows box to ESX, I use WinSCP. WinSCP is free and does the job well. However, CPU usage is very high when doing the transfer.

An alternative to WinSCP is Bitvise Tunnelier. It provides a secure shell and file transfer. CPU usage during tranfers is also better and transfer speeds are better as well.

Take a look at both but my preferred choice at the moment is Tunnelier.