The SMS meant nothing. I send them at least 10 times a week to random people when I'm drunk and/or bored. I've already done it twice to the girl I mention above and managed to turn it into a positive! If you take it so seriously she's going to be creeped out. I'd make it into a joke. Mention it to her, then propose. I mean proper marriage propose, get down on one knee and ask her to marry you. If she laughs, she has a good sense of humour, act hurt until she stops. After she stops, or if she didn't laugh at all, chide her for being weird and say you don't put out that easily or words to that effect.
Remember MSN/email is not an alternative to physical contact, but an added bonus. Don't say anything on it you wouldn't in real life either, or she may decide she prefers internet you which is a big decider to stay "just friends" for the rest of your life. Calm down and limit contact, but the contact you do have must be of A+ material. You have to make her want you too or it won't work out. If she's not laughing her head off or having a philosophical epiphany every moment you're there, you have failed. It's not about being somebody you're not, it's about being brave and level-headed enough to be the real person you are underneath, behind all the social stigma crap.
Don't get too drunk at the party. You want a buzz and enough to lower your inebriations, no more. Throwing up and bouncing off walls is not attractive. Drink slooooowly, and only a few cans. It's better if you drink spirits instead of beer too as they don't smell/taste as bad to girls, if you know what I mean. You want to be roughly one unit of alcohol above her at all times, no more no less. Be active all night, don't wait in the corner for her to be alone so you can pounce. Talk to her friends, laugh, joke, play games, whatever you crazy kids are doing these days.
You are the life of the party, believe it. If you do this right you two will be alone by default, parties can sense this kind of thing and adapt pretty well. Don't go all emo on her though, continue to be playful and do what's comfortable to you in flirting. Think of something funny then go in as if to kiss her, but instead put your head to the side of her and whisper it. The action will put the notion of you and her in the top of her head if it wasn't already and will make her feel a right goof if she thought you were actually going to do it, feel free to make fun of this if you do.
Then in a bit when your feel the time is right (before you pass out) you can go all romantic and look into her eyes, hold them, and go in for the real thing. Talking about relationships before they even exist is boring, but now you have a reason to, and hopefully a good one ;)