I have installed MacFUSE and ntfs-3g... without any problem... But how to I actually use it?

I have an NTFS volume with VISTA intalled, it mounts automagically on my desktop, but I can't write to it...

Cheers

you are bound to the NTFS format instead of FAT. But Mac OS X 10.4 can only read, not write, to these kind of formatted volumes. Follow these steps and you will be able to write to them as well:
1. If you choose to compile yourself, install Xcode 2.4.1, and especially the SDK package within it. Also, compile the latest release of pkgconfig.
2. Download MacFuse. Compile it yourself, or easier of course, is to download the binary .dmg file.
3. Download ntfs-3g and compile it -- there's also a premade binary .dmg if you prefer.
4. In Disk Utility, check out the device identifier (disk0s2 or something) of the NTFS volume, and unmount it.
5. In Terminal, type mkdir /Volumes/your_ntfs_volume, where your_ntfs_volume is the name of your NTFS volume.
6. Still in Terminal, type ntfs-3g /dev/disk0s2 /Volumes/your_ntfs_volume -o ping_diskarb,volname="your_ntfs_volume".

Normally your volume should be mounted. If not, type disktool -r and killall finder. To unmount, use sudo umount /dev/disk0s2. Use AppleScript if you want to facilitate mounting and unmounting.