[Xenon]

there are differences

specialcharacters changes the string and converts " ' < > and other into html code &lt; and something like that. they show up on the screen equal, but are different strings

addslashes just adds / before ' and " so they could be used inside a string for inserting into db for example

hope it clarifies it
it's hard to explain even in my nature language, and harder in english for me

hope it clarifiys