Certain songs of mine would really kick some ass if I were able to turn off the vocals. Is this possible with Windows Media Player 11? If not, which media player is it possible to do this with?
Question Two: Is it possible to combine two different songs into one? Even if only on a playlist, so there is 0% silence between the two songs. Need for one to perfectly and smoothly flow into the next.
Little help?
Taking your second question first: I believe the latest version of WMP does do crossfading - not sure if it tries to beat-match as it does so, but there are media players out there that do. I don’t have a recommendation, but the terms you’re looking for are cross fading and beat matching.
If the vocals are in their own, unmixed stream in the file, then it should be fairly easy to eliminate them, but that’s unlikely to be the case in most media files.
Otherwise, it’s not easy. There are programs that claim to do it, but I’ve never come across one that did it well in very many cases. If the music is mixed so that the vocals are central and all other instruments are off-centre, you can remove the vocals just by inverting one channel then mixing it down to mono, but it sounds pretty rubbish.
How would I go about checking to see if it is the case?
This is sounding more complicated than I was expecting. There’s not a just a button I press to turn off vocals? 
Question #1: No WMP will not do this. Either will Winamp or any other media player. It is possible using a free program called Audacity, but it is not a simple press of a button, and, like Mangetout says, it doesn’t sound very good. Here is a youtube tutorial.
Question #2: WMP has had **crossfading **for a while. Go to *View > Enhancements > Crossfading and Auto Volume Leveling *(That’s what it is in WMP 10 anyway)
One caveat: I learned while DJing dances and parties that crossfading is great unless you want to change the next song on the fly. Then very bad things can happen.
You’d have to get a utility that would tell you about the audio streams in the file, but it’s really probably not worth it, because I doubt there are very many files with vocals in a separate stream.
No, there’s not - because it really is quite a complicated thing to remove one instrument or performance once it has been mixed for release.
It’s a bit like asking if there’s a button on the oven to take an egg out of a baked cake.
That is an outstanding analogy. I am going to steal it and use it, if you don’t mind.
Thank you both for the sad, but enlightening truth. 
What do you mean when you say “certain songs of mine”?
Feel free - I don’t think it’s particularly original to me.
In truth, it’s probably a little bit easier to remove the vocals from a song than it is to take an egg out of a cake - some quite clever things are possible with audio processing nowadays - but the end result might still be a bit weird and of inconsistent quality between one song and another.
See my signature. Most any of the songs that make me wanna jam would sound even better to me without any vocals. Just straight up energetic instrumentals.
See if you can find Karaoke downloads, they have already done the work for you.
Yes, it is possible to remove the vocals from some songs. This is done using a technique known as out of phase stereo. For it to work, the song has to be in stereo, and the vocals must be present in both channels (i.e., not just on the left or on the right). Contrary to what acetylene claims, there are many free media players which have this feature built-in.* Depending on the player, it may be labelled “out of phase stereo”, “left minus right”, “karaoke”, or “voice removal”. Even if your software doesn’t have this feature, you can achieve the same effect by trivially rewiring your speakers; see the aforementioned link for instructions.