It sounds like MacOS is just creating a disk image file (.dmg I would guess) for the USB drive, which can then be mounted. I'm curious if you can actually clone an SD card, or just USB drives...SD/CF cards are usually treated differently than USB drives, and the MacOS clone feature is usually intended as a means of backing up literal external USB drives.

Windows 7 actually does have direct support for mountable drive images in .vhd (Virtual Hard Disk) format. You could create a VHD via the Windows 7 Disk Management tool, mount it, and copy the files from the memory card to your VHD (which, being a file, can be mounted, unmounted, copied for backup, etc.), and delete the VHD when you no longer need it. This would not be a 100% exact clone (although I suspect neither is the MacOS clone...its probably a new disk image with the contents of the external drive.) You could also use a backup tool like Acronis True Image to create USB drive clones, however it does not seem to support cloning SD/CF cards (at least, the version I have, 2011, does not.)

To create a VHD and copy the memory card contents to it, which would pretty much be as good as a MacOS DMG, do the following:

• Right-click Computer, choose "Manage"
• Expand the "Storage" node
• Right-click "Disk Management"
• Select "Create VHD"
• Fill out the form
  • Size XYGb (i.e. 16Gb)
  • Fixed Size
• Watch the status bar for progress
  • May take a few minutes...
  • Virtual disk will appear as an unallocated drive when done
• Right-click "Disk" (should appear bright greenish-blue, unlike normal drives which are silver)
  • Select "Initialize"
    • Use MBR format for greatest compatibility
• Right-click "Unallocated Volume" (should have a black "Unallocated" strip color)
  • "New Simple Volume..."
    • Next...
    • Next...
    • Pick a drive letter or mount to folder
    • Next...
    • NTFS or FAT32 (NTFS offers more features)
    • Add a Volume Label
    • Perform a quick format (Checked)
    • Next...
    • Finish
• The drive should automatically mount, ready for use

Once you have a VHD, you can just drag-and-drop copy everything from a CF card to the VHD. In windows, cameras themselves show up as devices in Computer. You can open up the camera, and directly access the memory cards inside them, and just copy the DCIM and any other folders across to the VHD. If you have a card reader in your computer, the cards will usually show up as removable drives once you pop a memory card in. You can again just copy the DCIM and any other folders across to the VHD. Cameras usually have pretty fast interfaces, and copy pretty quick. Some memory card readers for computers, particularly cheap ones, are often limited to USB 1.1 speeds, so you might only get a few mb/s out of them. USB 2.0 ones will usually get you about 20mb/s. If you have the option, even for non UDMA-7 memory cards, picking up a $20 USB 3.0 PCI-e card and USB 3.0 CF/SD card reader will get you about 40-50mb/s (and significantly more, up to 150mb/s, on todays native UDMA-7/USB3 compatible CF cards.)