Is my internet good enough to run a lag free minecraft server?

You can run a 100 player probs

Thats awesome, glad to hear that (I posted this thread)

Zenn22 doesn't know what he's talking about. I have a dedicated Ubuntu server running a Minecraft server and 110 Mbps download and about 12 Mbps upload. Do a little research in the Minecraft forums and you'll find the math to calculate the most users. Mine will support 25 to 30 users max with lots of lag. Typically there are about 6 users on it and all I hear about is the lag.

The performance of your Linux server is important, too. I have pretty decent hardware, but improving it would reduce the lag.

The upload speed doesn't matter much, it's the ping and your packet loss, if you're on an ADSL the line attenuation rate, is more important of a factor than the SNR in your packet loss, the less the packet loss the better the game experience, some people from australia have higher ping than people from iran and pakistan but they still get to play