You will be fine. I suggest you tell everyone you are married to your boyfriend, but DO NOT go to the trouble of wearing rings (not common enough here that anyone will check) nor using his last name (not done here so no one will question that). All you have to do is refer to him as your husband and him refer to you as his wife. THAT IS ALL you have to do.
It is probably better if the two of you are together most of the time, but you should be OK, if you dress respectfully, but that doesn't mean you have to cover your head - just don't go outside braless and in a sleeveless top and shorts. In Feb you should be in jeans and wind cheaters anyway - it's cool here - especially since you will be coming from your summer - you will feel it is cold. And don't flirt, even mildly, with the Egyptian men. They take it way too serious if you do and it's difficult to explain "kidding" to them. LOL

The hotel I would recommend for you is the Mayfair Hotel in Zamalek. It is a cheap hotel, owned and run by Canadians. The neighborhood is the best one for being out and about alone. Zamalek is the Cultural Center of Cairo and where about 80% of the worlds embassies have located so it is a very International neighborhood and safe. The web site is
http://www.mayfaircairo.com/
You can find cheaper hotels in downtown Cairo, but you will pay more with stress and bothersom touts hitting on you.

Have fun.

I have to add - if I were you, I might wait to come to Egypt until you can afford to do more of Egypt while here. To come ALL THE WAY from Oz and only do Cairo, seems kind of a waste. While I live in Cairo and love Cairo and could stay busy in Cairo for 9 days, the only reason I'd say this is worth the plane fare is if you intend to come back some day. You are young, so maybe this is just a recon trip to see if you like Egypt enough to come back. The problem with that is that many people much prefer Upper Egypt or the Red Sea to Cairo and if they only see Cairo, they may think it isn't worth another trip. If you can wait another year and save enough to see a bit more, even if quickly so you get a better overview of what is here and everything, I think that would be better.

Thanks so much for taking the time to write such a helpful reply! Definitely met the 'putting my mind at ease' criteria. The reason we're making such a short stop in Egypt is simply by chance - we're spending several weeks in Kenya and Tanzania and it just so happened to be cheaper to fly via Cairo than directly into Nairobi for some reason, so we decided we might as well stop and have a look around. I've always wanted to visit Egypt but didn't think I'd get the chance any time soon, so when the opportunity came up I just jumped on it lol. We're really time-poor more than we are money-poor on this trip, but I'll probably be making the trip to Tanzania fairly frequently over the next few years (have family there) so if Cairo proves to be a good route I might even become a regular visitor!

What would you/anyone else reading recommend as must-sees in Cairo, besides the obvious (Pyramids, museum etc.)?

I know you said you'll only be spending time in Cairo, but I agree with Deb - do whatever you can to at least add Luxor to your visit -- we enjoyed Cairo's sights, but loved Luxor's.

BTW, as a tourist, I would NOT have wanted to spend 9 days in Cairo. We had four and it was plenty.

I would have Debbie from Causal_Cairo as your tour guide while in Cairo.

Dds71@aol.com

Have a good time in Kenya and Tanzania ( I was there a couple years ago on a Safari).

What to see/do besides the Giza Pyramids and the Museum? This depends on YOU and you alone. What do you like to do/see when you go anywhere? Do you want to learn to cook? Do you like looking at old buildings? Do you like to shop? Do you like to camp? There is so much you can do, that like I said before, we could keep you busy for 9 days around Cairo pretty easily.
If you are not so money poor that you could afford a nicer hotel, the Longchamps (http://hotellongchamps.com/) is by far the best value and still an economical hotel. It also is in the best neighborhood of Zamalek. They fill up fast, so if you want to stay there, don't delay in making your reservations.

http://hotellongchamps.com/ The link in the post above isn't working well for me. I don't know if this one will better. IF it does not, then Google Hotel Longchamps Cairo and see if you can get to their website more easily that way. It is worth the effort to find it.

Ah ha! It is the ) at the end of the link in the other post that messes up the link address. The second one works fine. Wish we could EDIT our posts here at FODORS! Hey Mr or Ms Monitor - can you ask your techy people to make that change?