There seems to be a lot of misinformation on this thread, so, in no particular order:
1. A .tar file is the standard way to make archives on Unix and Linux machines, just like .zip is a standard on Windowqs and .dmg and .sit are standards on Macs. Tar files are occasionally used on Macs, because OS X is built on Unix. Tar files aren't often used by Apple, but remember that Java is not made by Apple, and Apple just passes along Java updates from Sun (the people who created Java).
The file should not have been 47 GB. This is bigger than most laptop hard drives are! A file that shows up as 47 GB in size would be absurd; I would suspect serious disk directory corruption. Check the disk with DiskWarrior or Disk Utility.
2. A pattern of vertical lines on a computer display usually indicates defective hardware--specifically, defective VRAM. Run the Apple Hardware Test CD that came with the computer.
3. In Mac OS X it is not necessary to keep 15% of the drive free. The Micromat page is outdated.
This "requirement" had nothing to do with HFS+. The reason for this requirement had to do with a bug in Mac OS 9. In Mac OS 9, if a file was saved to the disk in many chunks, and the part of the directory that keeps track of multiple chunks of a file needed to be expanded but could not because there was not enough contiguous free space available, the Mac OS 9 File Manager would not return an error message. Instead, it would stomp all over the extents allocation table. This was an OS 9 flaw that has been fixed in OS X. In OS X, this will never happen. If this situation arises, you will not lose data--you will just see an error message telling you that the file could not be saved. (This has been extensively discussed, including by a Micromat technician, over on the MacFixIt forums.)
OS X requires at least 5 GB free on a startup volume, because the virtual memory system can allocate, at most, 5 GB of swap space. In addition, as you work with programs, you need enough space to be able to save your files and so on. But the requirement to keep 15% of the drive free--which was always more of a guideline than a rule anyway--is no longer relevant to OS X. Even if you use OS 9; in OS 9, it still uses the OS X File Manager to save files. The rule is only relevant for computers booted into OS 9.