It runs "perfectly" but since it was written in 2007 I don't think they made the API calls to disable folder redirection. Otherwise if it's a 32 bit app, the SysWow64 is going to redirect accesses to some system folders. For example C:\Windows\System32 accesses are redirected to C:\Windows\SysWow64. It doesn't matter really for normal use to see which folders you left too many videos in. But if the malware by chance is 64 bit then it might be overloading the System32 folder. You won't know that if you measure the size with a 32 bit app since you'll be actually measuring the file usage in SysWow64.
Maybe a bit unlikely, but for diagnostic purposes I think it's safer to use a native 64 bit utility to actually see what's what.
Also I'd advise using some malware scan from a boot CD. Running something from inside the account that works might not detect the malware that seems to be in the kid's account. Makes sense as kids are usually less cautious about surfing. Better to scan the whole drive from an isolated boot CD OS. For m8000n the vanilla Sata disk drivers
on a boot CD should be fine.