I think I should have made myself clearer: I really don't care whether a super-computer or a server or whatever would do better than 20 1.5GHz CPUs.
I don't have the money to buy a super-computer and build a computer-game for it, but I do have a network of 20 computers with 1.5GHz CPUs at school, which are already there and are gonna cost me nothing to experiment with.
I'm wondering whether I could create a game considerably more advanced than what we have today and test it on those 20 computers.
My uncle has an internet-cafe with good computers.
Imagine what if I could pull this off! I could run the super-game on those computers and charge money from rich people to try it out.
Is this possible? Is it actually worth a try?
I have absolutely no experience with this stuff and I was hoping that someone could tell me whether my idea is realistic...

I've read half the replies before I got bored and wanted to add my own 2 cents (so it may have already been answered...)

I would say that your current machine (where the game is being played) would need to do basically 100% of the graphics math. Reasoning is that you can do a few gigaflops (gigaphlops?) per second on many newer machines, which means you can update your player's "move-left" command quickly enough that there doesn't appear to be [much] lag. You don't want to tranfer that amount of data across a network; there would be too much lag.

However, the AI part, or updating non-visible portions of the screen COULD be calculated elsewhere. I know that Google uses clustered machines to do its searches and webcrawling, and that large game servers can often cluster their machines together to take care of all the different players' positions and game rules.

I'm saying that having the server keep track of all the non-rendering portions of the game might be the way to go: if you have multiple computers crunching the numbers, then the one the player is sitting at would take care of movement and graphics updating, and the other machine could be loading the next "grid" of the current map and feeding that data directly into the player's machine (so no disk access needed, and all the levels could be pre-calculated, further reducing CPU time).

EDIT:
Jonatan Hedborg, ugh! Imagine if the Sims ever got wind of something like that. Entire villages being created and interacting with 100% accurate AI simulations with each other...