VMWare does not work well when its multi-gig virtual machine files are located on a USB hard-drive. At least in my experience. The guest machine operates slooooow and sometimes becomes non responsive. Again, this in my experience across several laptops and desktops. But it's easy to test and try, just copy the files and go.

I haven't tried eSata HDs for this as metioned above, but based on what I've seen using USB drives, I'd be suspicious until I see it working acceptably.