[root@boost VirtualBox VMs]# du -h --max-depth=1
17G ./Windows XP (Other)
21G ./Windows XP
26G ./Windows XP (RE)
11G ./Large Vista (Base)
13G ./Windows Vista (Other)
17G ./Large XP (Base)
8.7G ./Windows 7 (Other)
7.0G ./Large Windows 7 (Base)
21G ./Windows XP (Visual Studio)
I highlighted the important lines for you. A base install of Windows 7 with ALL the updates, takes up 7G total, not much diff to your 6.1G lion install. (The XP base image size doesn't count for offtopic reasons).
Is that Win 7 Ultimate or Home/Home Premium?
Also, having your two finger scroll inverted is seriously not fucking cool. Going to help someone on their Mac, and having to adjust for their inverted settings is fucking irritating.
You can uncheck 1 box to "revert" it.