You will need:
Windows Home Server (Or an SMB network share) with free space as big as your mac's HDD used space
Apple computer running 10.4 or 10.5
Network Connection between the two
I have not tried this with 10.4 Tiger, but i know its much easier than Leopard.
Step 1: Enable SAMBA Backup on the Mac
Step 1: Open Terminal
Step 2: Type the command:
"sudo defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1"
with no quotes. Then type in your password.
You have enabled Time Machine SAMBA backup.
Goto Step 2 for Leopard, or skip step 2 if you have Tiger
Step 2: Create the Backup Image (Leopard Only)
Step 2: goto File => New> => Blank DIsk Image...
Step 3: A Box will pop up. Fill it out with the following information
Replace #ComputerName# with your computer's full name with all Symbols and correct Capitalization (ex: Steve Job's Macbook)
Replace #MACAddress# with your computer's mac address, making sure that all letters are lowercase
Save As: #ComputerName#_#MACAddress#.sparsebundle
Volume Name: Backup of #ComputerName#
Volume Size: The maximum size you want the Mac Backup to ever get
Volume Format: Mac OS Extended (Case-sensitive, Journaled)
Partitions: No partition map
Image Format: sparse bundle disk image
Step 4: Hit "Create"
Step 5: When it is done creating, copy the ".sparsebundle" file on your desktop to the root of the target SMB share
Move onto Step 3 =>
Step 3: Backing Up
Step 1: Make sure the target SMB share is mounted on your Mac
Step 2: Open System Preferences and go to the Time Machine section
Step 3: Select "Change Disk..." and then select your SAMBA Share
Step 4: When your computer starts the initial backup (in about 5 mins. of you changing the disk) it will take a while, so let it sit overnight. every backup after that will be seamless and under 5 mins long, without you even noticing its backing up.