Virex... what? How does admitting feelings for a friend make you "the kind of guy who only befriends girls because he wants to screw them"? And what is really wrong with that anyways, if you recover well? Hell, one could argue I'm friends with MOST of my friends because I wanted to screw them at some point. I'm not sure why that's an auto-lose.
Anyways, assuming she is potentially interested, flirting is the way to go. Ask her to spend some quality time alone with you. Go with the flow, and most of all don't be afraid to either back off and forget about OR outright admit your feelings if things don't seem to be going your way. (the first gives the best chance of the friendship continuing if you value it most highly, and the second gives the best chance of something more happening but might compromise the friendship) Only you can decide which is more important to you.
Generally, though, flirt. Flirting always skirts the "creep" border, of course, so make sure to stay aware and make sure she's responsive. Its a fun game to play, but only if both parties are interested. And remember that being interested in flirting doesn't necessarily mean she's interested in something more - eventually you WILL probably have to make an overt move (or she will, but someone will at least)