I would like to see some examples of proteins with PDB ID so that I can download and see them in VMD software. I need some proteins with alpha helix only and proteins with beta sheets alone.
You may consider taking a look at the SCOP structural classification of proteins to check all beta proteins and all alpha proteins. As per specific examples and though not belonging to the SCOP classes mentioned above, Porin for a beta protein (PDB:1A0S), and Rhodopsin for an alpha protein (PDB:1F88) are two nice structures to look at.
You can find examples by using the "drilldown" function at the RCSB PDB homepage:
Click on the number 103921 at the top of the page at http://www.rcsb.org then find the "SCOP Classification" section and then e.g. select "All alpha proteins".