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 :)

It might not matter in your case, but this will only catch comments that start and end on the same line, as the '.' does not match the newlines.

You can try these:

$question =~ s/\*.*?\*//sg; # the s modifier causes . to match newlines

or

question =~ s/\*[^*]*\*//sg; # [^*] matches the newlines too

Update: added a * in the second regexp (thanks swiftone) and removed the (), you don't need to capture the comments.