Hey man, nice post!
Ah, the high school days... if only I knew then what I know now, I would have understood how women work enough to be able to handle these situations when they arose, and/or recognized them for what they are.
Here's my mantra, and something that's good to live by: when women like you, they HELP you, and don't do things to try and confuse you. They let it be known they like you, and are willing to do the things necessary to make sure that, at the very least, you ask them out.
So, let's look at your situation, shall we?
1. "I don't know if we're just friends or could be something more." - The only way to ever find this out is to: (a) ask for her phone number, (b) ask her out, (c) make sure she goes on the date, and (d) see how she reacts at the end of the date when you go for the kiss.
That's pretty much it. But the important thing is that you (b) ASK FOR THE DATE. You can "hang out" and/or see her at parties all you'd like, but you need to get that one-on-one time to see if the sparks aren't just coming from your imagination.
2. "Right now she's kind of with someone." - That means that, for the moment, she's OUT. Despite what movies like "Twilight" would have you think, a girl can't really split her interest level equally between two guys, and the one she has a higher interest in is always going to pull rank. And right now, it's not you. How do we know this? Read on...
3. "I was at a party and we were touching each other a lot and holding hands a little bit, but she left later on to go be with this other guy because she felt bad for being with me so much." - This is why. What she told you was a "lie." Think about how illogical her argument is. She was having such a good time with YOU that she had to LEAVE you to hang with another guy? No, what happened was she was enjoying the attention you were giving her because the other dude wasn't around. Then she realized she'd rather get felt up by him and left you hanging out to dry. Just 'cause a girl is touching you or holding your hand doesn't mean she wants you - that's actually lightweight stuff. Were you fondling her boobs? Kissing on her? If not, eh...
4. "Also her friends have told me she thinks I'm hot..." - Yeah, about that: NEVER LISTEN TO FRIENDS, THEY WILL F--K UP YOUR CHANCES WITH A GIRL. Plus, just because she thinks you're hot doesn't mean she'd date you. I think Halle Berry is hot, but that chick is crazy - no way I'd try to wife her up. It's high school, so I'm sure her and her girlfriends were probably just ranking the various guys they know and your name came up. Congrats, you're one of 10 guys she probably finds hot.
5. "After the party we were texting until early in the morning." - That's great. You know who else she texts for that long? Her GIRLFRIENDS, which is what she's probably viewing you as. Don't get into the habit of being a chatty Cathy with girls via messaging services. Texting KILLS relationships, as well as a girl's feelings for you for a plethora of reasons - appearing too available, miscommunication, giving away too much info about yourself... I could go on.
Bottom line, though, is that if she wanted to be with you, she'd make it obvious enough for you to tell. But if you're looking for a way to figure it out, just ask her on a date - say something like "Hey, I was going to see a movie this weekend and was hoping you'd join me." She'll either say "Yes" (or if she's busy she'll counter-offer with a different day and time, which is still a "Yes); or, she'll give you a multitude of excuses as to why she can't go, which you should interpret as a "No." Regardless of how she responds, don't take it personally and respond as if you're indifferent.
Hope this helps!