It's definitely beatable, but if you rush, you probably will fail
I haven't tried to get a good time in the intermediate/expert levels, but the easiest one goes trough in about 12-15 seconds, depending on the start. Not that I play it every day, but sometimes for fun.. (the Windows version I mean; on Linux there's always a lot better things to do even when there's nothing to do).
I've also heard rumours of how you can cheat in minesweeper (see if there's a mine under the cursor without clicking), but if you did, why would you even play -- for the fun of clicking?
Just keep trying, patiently, and eventually you will win. In some cases you can win by measuring the places of the mines based on the numbers, but in some cases the game might end up in a situation where you just need to guess. That's easier than thinking, of course.
yeah, I won the game in 1 second, but that required setting up the biggest game field available with the least mines - one click beats the game. Playing minesweeper for killing time is all right, but playing it for the records is..umm..well, take a look out of the window and you should see.