Hi, I understand that you obviously want as many backups as possible with Time Machine in the event something gets jacked up. I have a 1 TB Western Digital Caviar Green HDD (5400RPM, 64MB Cache, SATA) in a USB HDD External Enclosure that just arrived today from Newegg. Eventually, my current Desktop (running WinXP SP3) will be replaced with an iMac this year, after the new model gets released. Other computers in my house include a Gateway Laptop also running WinXP SP3 and my iBook G4 running OS 10.4.11. I was planning on splitting the HDD 60/40; 600GB would be formatted in HFS+ format and used purely for Time Machine backups, and 400GB would be formatted in NTFS format and used for data (music, pictures, important documents.) At this time on my Desktop, I have a total of 320GB of storage space (2 160GB Western Digital CaviarSE HDD's on RAID-0) and I'm only using about 85GB of that, which includes a few monster games (World of Warcraft is taking up 25GB, Steam games take up around another 10-15GB.) I need this external drive to be available to all my computers to keep a safe copy of documents, so here is the meat of the question: How much space does Time Machine actually use? Would it be more beneficial for me to change the partition to something other than 600GB/400GB as I planned on doing? Is it better to download the Third-Party files for the Mac to read/write to NTFS, or for the PC to read/write HFS+, or both? Thanks in advance!