nkarasch, your situation sounds just like what I went through a few months ago... I wound up having a torn meniscus. I was dorking, bent my knee slightly sideways after falling off a little rail, and immediately felt a very brief but sharp pain, followed by a small amount of discomfort. I felt like my knee had a little extra "give" to it, but I went on to skate for a while afterwards until I was tired.
I went to bed later that night, then was woken up at three or four in the morning to excruciating pain and swelling... it felt like I had acid running around in my knee and boiling water on top of it, totally fucked. I hobbled, went to the doc, nothing showed up on the Xray but the MRI showed the tear.
I had surgery, and I'll just tell you what Thiebaud and Cliff (here) told me... it's the easiest knee surgery you go through. Three small incisions, the doc trims the tear, and you sport some sutures for about a week while keeping your knee supported with a wrap or a light brace (and regular ice and ibuprofen).
After the sutures are taken out (roughly a week or so), you'll be able to skate (within limits) right off the bat because the meniscus doesn't really heal or anything... it's just a little pad of cartilage. You might have a *little* bruising and soreness from the surgery, but nothing that will really have an effect on your skating. There's really nothing you can do to your knee to reverse the fix that the surgery provides, though you can always re-tear it... you're not more susceptible to tear it again though.
The surgery is walk-in, crutch-out in the same day, and the crutches are only for a day or three depending on your doctor's advice. You can also get pain meds that you won't realistically need.
Of course I'm not diagnosing your shit (see a specialist as soon as you can) and make sure. If it is your meniscus, start riding a bike to ensure that your knee is as strong as possible post-surgery. I had mine done just a few months ago and I figure on transition I'm 100% back (which is mostly what I skate), on street I'm about 90% back... if only because I don't like to risk big jumps down shit. Then again, I'm 33 and pretty haggard medically speaking (past injuries and whatnot), so if you're younger you'll be bouncing back in absolutely no time at all.
Make sure you see a specialist before you do any bike riding or swimming though. Hopefully it isn't your ACL, as Lance basically said it's a bit more complicated of a recovery (not an injury I've had, knock on wood), but before I knew for sure, Thiebaud reminded me that half his guys wreck their ACLs on a regular basis and still kill... namely Trujillo.
Good luck man.