Originally Posted by Kael'thas Solo
I would have applied at several places and when I got called for an interview give my two weeks. That way you're not like... "oh well, i'm still working for this other person and I haven't given my two weeks notice... and uh..."
I wouldn't hand in my notice simply because I'd been invited to an interview - there's always a chance it won't be successful, and might leave you in an awkward situation with your current/soon to be ex-employer.
As for interviewing while still employed, I don't see anything wrong with it, but I'd try to make sure it was at a time that didn't disrupt the job I was doing at the time.