So, let's say hypothetically that I made this kick ass game,
right? Okay, but it wasn't finished. Anway, then I decided to,
hypothetically, post it on a website and get some feedback
on my progress.

Now, this game works flawlessly on my machine. Well, as
I expect it to, anyway. The framerate is consistant; control
is fine. It also works that way on one of my friend's machines.

However, I have another friend who I let try it. He came back
and told me and it was all kinds of suck. He'd hit a key and there
would be a huge delay before anything happened.

Oh, then I start reading all these replies to my feedback thread
that agree with friend #2; that the game isn't running well. Huge
framerate drops. One lady even said that it almost crashed her
computer.

There are really two different versions of the game; both are
pretty much the same other than the fact that one was complied
with VC++ 6.0 and the other was compiled with VC++ 2005 Express.

So, hypothetically, what the hell is wrong? Why won't it work the
same across all machines and how do I fix it if I only know how it
runs on mine?

All hypothetical of course.