A/G BLAST is an enhanced, Macintosh-specific version of NCBI's
standalone BLAST (Basic Local Alignment Search Tool) application.  It
requires a G4 processor and OS X, and will not run on other
platforms.  BLAST itself includes several applications for similarity
searching between sequences, and while the A/G BLAST distribution
includes all of the tools found in the standard NCBI BLAST, the only
enhanced tool is BLASTn, which finds similarities between nucleotide
sequences.

A/G BLAST is available as an executable (blastall.gz).  If you are
already using version 2.2.2 of standalone BLAST, then you can simply
replace the "blastall" executable with this file.

In addition, the entire source package is available (AGBLAST.tar.gz).
A/G BLAST is derived from NCBI's BLAST version 2.2.2, and can be built
in the same manner. If you are building BLAST from the source archive,
the build script can be found at ncbi/make/makedis.csh.  For further
instructions on building and using BLAST, see NCBI's BLAST demo at:

ftp://ftp.ncbi.nih.gov/blast/demo/

More general information about BLAST can be found at:

http://www.ncbi.nlm.nih.gov/BLAST/

which includes a tutorial on using BLAST.

Note that installing A/G BLAST will not have any effect on BLAST
searches performed through a browser (WWW BLAST) or search queries
submitted to NCBI's servers (Network BLAST).  The changes only apply to
the standalone version of BLAST.