Registry. Go Bleeping Computer to find out.
The way files are named. 8.3 convention in 9x and ME, long file
names and long extensions are accepted for NT onwards.
Command line interface. MS-DOS commands and Command Prompt commands
are different. Go and try that out.
File system used. NTFS for Windows NT onwards, FAT, FAT16 and FAT32
for Windows ME and below.
Networking abilities. Too obvious. You will find networking in NT
and above machines easier, whereas for ME and 9x, you will run into
some trouble.
Drivers. Too many drivers.
The way folders are organized. In XP, it allows you to view in
groups, other than the other options.
Searching. Indexing is better in XP than the other versions. Also
got one stupid dog.
Built-in firewall for XP SP2.
Locking down of programs (IE, WMP, Windows Messenger) in XP (you
can't remove it, whereas in other versions, it's possible)
Windows critical files are protected. If you accidentally delete
them, they will auto generate themselves back (like viruses).
That's only for XP if I'm not wrong.
