They will both make the text invisible, but display: none; will make it look like it never existed, where opacity:0.0; filter:alpha(opacity=0); will make it look like something is just missing.
For instance.
display: none;
This is text
This test is invisible
This is more text
will display as
This is text
This is more text
opacity:0.0; filter:alpha(opacity=0);
This is text
This test is invisible
This is more text
will display as
This is text
This is more text
Make sense?
