To get into Basic Stamp I all you really need is the Editor, Manual, Cable, and Stamp I itself.  I highly recommend a solderless breadboard to make learning a lot easier. All information needed including the Editor and Manual can be downloaded from www.parallax.com or Steves workbench at www.radioshack.com .  To build a cable get your self a plain jane printer cable and cut off the end that would normally go to the printer.  Now find pins 25, 11, 2 from the cable and attach them to pins 2, 3, 4 respectively on the stamp module - that's it!  You can get a stamp module from almost anywhere, I got mine from Radio Shack for $34 if you hunt you can get them cheaper.

    Read the manual, don't worry if it's over your head at first.  All you really need to do is make sure you have your pins connected properly, understanding how to program will come with time and practice. 

    For your first program you write and download into the stamp make it simple:

Dirs = %00000000  'Make all pins outputs  

main:                        'program start

Pin0=0                    'pin 1 will be low (ground)

Pause 1000             'wait 1 second

Pin0=1                    'pin 1 will be high (5 volts)    

Pause 1000             'wait 1 second

goto main                'start over from top

Now if you connect an LED and resistor in series to I/O pin 1 on the stamp, that LED will flash on and off once per second.  Wee haa, not very cool but it is a good test to ensure everything is hooked up correctly.  Now realize that the 8 I/O pins on the Stamp I are labeled Pin0 through Pin7, sooooo this means Pin0 is the first I/O pin on the Stamp.

ADDITIONAL NOTES:

    I have found another maker of a 'Stamp' like product at www.basicx.com and it's only $19.99 per module although this time you really need to buy the starter kit for $100.  The module is much more robust with a huge jump in processing time, memory, networking multiple chips, total code allowed, etc.  Once you have 'Stamped' I highly recommend looking into Basicx for higher level projects.  After that it is time to move on to PIC and related microprocessors, they are much cheaper and can generally be a better alternative.