1. Download and install MacFUSE for Mac OS X 10.5This approach work on my Mac OS X 10.5 + 10.5.1 updates and Windows XP SP2 with NTFS partition on MacBook Pro (Model Identifier MacBookPro3,1).
2. Download and install NTFS-3g for Mac OS
3. Restart! If you are lucky you can try read and write your Windows' NTFS partition now.
Before you decide to proceed, google "read write NTFS Mac OS X leopard" to be informed of newest advancement and check for latest versions of MacFUSE and NTFS-3g.
Reference
1. MacFUSE http://code.google.com/p/macfuse/
2. NTFS-3g http://www.ntfs-3g.org/
3. NTFS-3g for Mac OS http://macntfs-3g.blogspot.com/
4. Filesystem in Userspace http://en.wikipedia.org/wiki/Filesystem_in_Userspace
5. Filesystem in Userspace http://fuse.sourceforge.net/wiki/index.php/FileSystems
6. NTFS on your Mac http://www.tuaw.com/2007/11/19/ntfs-on-your-mac-two-ways/