TeX Live 2008 is available online now, and will be available on DVD in September 2008 (depending on production and mailing delays) and sent to members of most TeX user groups.
If you wish to obtain TeX Live through TUG, please become a member of TUG. The TeX Collection, including TeX Live, is distributed as a benefit of membership to TUG members each year. You'll also receive a year of TUGboat, among other things. (Alternatively, you can purchase any of these items from the TUG store, without becoming a member.)
Most other TeX user groups also make TeX Live available to their members; please contact whichever you are interested in for details. TUG encourages you to join whichever user group is best for you.
For typical needs, we recommend using the small network installer package mirrored throughout CTAN. Specifically, to use the network installer, download one of these files: install-tl.zip for Windows (3+mb), or install-tl.tar.gz (1mb) for everything else. (The .zip archive works fine on all platforms; the .tar.gz simply omits installation support programs needed only on Windows, the two archives are otherwise identical.)
After unpacking the archive, follow the installation instructions.
You may want to get the ISO image instead of using the network installer, for example, if you want to burn your DVD. It is around 1.2GB compressed (md5, sha256 checksums). You can:
The image is compressed with lzma. The results are much superior to zip (or bzip2 or gzip), and for the file this size, it's worth it. If needed, get the sources for lzma utilities and/or the lzma binaries, including Windows, that we've compiled for TeX Live. From a command prompt, run lzmadec <texlive2008.iso.lzma >texlive2008.iso to decompress it. If you prefer a Windows GUI interface to deal with the lzma files, try 7-zip, version 4.58 or later.
After mounting the image (typical invocation on Unix:
mount -t iso9660 -o ro,loop,noauto /your/texlive2008.iso /mnt),
follow the installation instructions.
The uncompressed ISO is not available from tug.org; it is too wasteful of our host's bandwidth.
The contents of the release image are also available as large compressed tar files on tug.org, primarily for the benefit of distro maintainers: texmf (the texmf trees), source (the TL-specific sources), bin (the binaries distributed with TL), and extra (miscellanous other files). Please don't download these from tug.org unless you know you need them.
The last general update of packages and programs for the 2008 images was made on 16 August 2008. However, unlike previous years, we will be continuously updating packages in TL as they are released to CTAN. To install any or all of these updates, use the tlmgr program. tlmgr also provides many other TeX installation options and features, explained in the tlmgr documentation.
Although it is possible to update, it is certainly not necessary. The set of packages and programs that were included in the official 2008 release (and burned onto DVD) will likely suffice unless you know you specifically need updates made since then.
Finally, Older releases of TeX Live are available for historical purposes.