How to download Blast to your own computer
Explanation and notes
Go to This is the National Center for Biological Information (NCBI) site, home of Blast and much else
Scroll to bottom, 
Click on FTP Site (left hand bar)
Gets you to page where you can download  programs NCBI makes available
Click on 
> BLAST Basic Local Alignment Search Tool
(avoid the Blast button at the top of the page). You should get to an index.
Click on Executables This opens an index of programs
Click on blastz.exe Blastz.exe is a file that contains all the programs and data files necessary for Blast to run under DOS (or in Windows). (If you want Blast on something besides a PC, you're on your own.) Your browser will ask you where you want to put the file.
Click on Save in box. Click on C:
Click on new directory icon (a folder with a sun peeking through).
Type Blast in the name box, press Enter key.
You're free to download Blast anywhere you like, but be warned: LOTS of files will be created. I suggest a new directory
Click on the directory Blast that you just made. Common error: Making a directory doesn't put you in the directory.
Click the Save button Saves Blastz to C:\Blast directory. This should take a few seconds, or much longer, depending on your connection.
Get to a DOS window 
(Run Command or Run Cmd)
Blastz is a DOS-based program. You can't run it directly from Windows.
Type CD \Blast Change directory to Blast, where you put Blastz
Type Dir (not necessary, just to get immediate gratification). You should see something like
BLASTZ   EXE     7,808,692  09-10-02  4:14p
Type blastz Blastz is a self-extracting program. Running the program decompresses all of the files within it. You should see lots of messages like
inflating: readme.bls
Congratulate self You're done!