I have no information here, but I wouldn’t be surprised if in 2003 Windows had an order of magnitude more code in it than a Linux distribution. Don’t forget, back then, Windows NT had support for these runtimes: Win32, Win16, DOS, and POSIX. Also, Windows had drivers for a lot more hardware than Linux did. Add in all the management stuff (Active Directory came about around this time), and I think it almost had to have substantially more code than Linux.