There are a couple of ways to get data from IRIS/DMC in Seattle, Washington:

The best way to get familiar with the options that IRIS/DMC has to offer would be to telnet into their bulletin board--

telnet dmc.iris.washington.edu
login: bulletin
password: board

The text will explain the different ways to access the data.  The "breq_fast" request mechanism is probably the easiest method for obtaining data.

If you would like to look at sac files from recent events, there is an easier way to get data by ftp-ing to the same address.

ftp ftp.iris.washington.edu
login: anonymous
password: your_email_address

cd pub/gopherdata/data1995

When you do a "ls", you will see the various events sorted by origin time.  From there, you can "cd" into the event of your choice, and "get" as many files as you want.