Second, I'm not sure I understand your question. Are you trying to remove /*This*/
Or turn it into //
Or are you just trying to get rid of *This*?

Assuming the latter, s/\*[^*]*\*//g should do what you want.

The trick is that in a matched pair (<>) you can use the presence of a starting tag (<) to stop a greedy match from eating the rest of your regexp. In an unmatched pair (*foo*) a greedy regexp will consume everything until the final matching element. So we switch to non-greedy matching with a dot star, or greedy without consuming our match (the [^*])

I hope that answers your question.

Update: Death to Dot Star! is an excellent discussion of greediness, the greedy dot-star, and why non-greediness isn't always the best solution.
Update2: Removed my non-greedy match that was in defiance of my own advice :)