If you want a copy of the Windows XP IFS Kit, you'll have to order it. Microsoft is NOT automatically sending updates to developers who licensed the Windows 2000 IFS Kit.
The XP IFS Kit contains:
1) Source code for CDFS
2) Source code for FAT
3) A "filespy" example (a lot like the well-known FileMon utility)
4) A generic file system filter example
5) Two sample network providers
NTIFS.H - The header file necessary to build file systems.
All this, plus documentation on a significant (and growing) number of otherwise undocumented functions, and machine-readable copies of 16 OSR-authored documents on file system development.
Oh, you also get everything that's in the XP DDK. To order the kit, or for more information, visit: http://www.microsoft.com/ddk/ifskit/xporderinfo.asp