macro: use selected characters

I want to create a macro that will allow me to highlight characters in a cell, then do the equivalent of:
Format > Font> Superscript

Here is my macro:

Please Login or Register  to view this content.

But it doesn't like the With Selection (i get an error). how can I get it to do the operation on the selected characters?
Thanks.

Look up the Characters property in VBA Help:

Please Login or Register  to view this content.

It looks like Andy's correct.

I used the suggestion from shg, and got a macro to work that superscripts the entire cell, but the inability to run a macro with the characters selected seems to be a deal-breaker