still confused, don't all the blocks go through the nodes?
Eventually, yes. But you need to know how the standard client works. It follows the longest, valid, chain. So lets assume you are evil miner 1. You have a significant amount of hashing power, say 10% of the network. One in every 10 blocks is yours.
Statistically, in this case, you're mining one block every 150 seconds. But that's just statistically. You will quite regularly, mine 3 coins in a row. You can re-write your miner to NOT follow the longest valid chain. You can tell it to keep persevering with your chain until you're 4 blocks behind the rest of the network, before you abandon your tree.
And when you DO get those 4 coins, suddenly the chain you're on is the longest chain, and you've just invalidated (orphaned) those 4 blocks that other people mined (and, whoops, those were confirmed by the network, too!) and you've just done a very small, but very easy, 'traditional' 51% attack with only 10%. Consider it brains vs brawn.
There are other things you can do, too. You can just ignore blocks mined by other people, too. Let your miners run for an extra 5 seconds on that block before you switch to the next one. See if you can get a block too. Keep mining that one. If you're lucky, you'll beat the other chain, and orphan them.
It also helps (as in, helps nasty-miner-1) other miners having slower nodes, too. At the moment, it can take up to 15 seconds for a block to propagate throughout the BTC network. I haven't done any timings on LTC, but I assume it would be roughly the same. Having a fast, central, node, means you can be an entire block in front of everyone else.
Oh look, I'm doing BTC-hacking 101 in this thread. Most of these issues are dealt with (by BTC and LTC) by having slower block times, and longer confirmations. As I said originally: Randomly changing numbers without knowing what the numbers are for is just a dumb idea.
