Not nessasarily - If you only intend to stay in Sharm, you dont need a visa. Just write 'Sinai only' on your entry permit that you will be given on the aircraft.
I'm going to Egypt in morning staying at Hurghada just down from Sharm. You can get visa when you land I think its �10, when are you going? I'm trying to find out what the weather is like at night been there in September not to bad but not this time of year?