Minecraft – the saturation of /feed

Are you running the 32-bit version of Java? If so, download and install the 64-bit version. 32-bit Java has a fairly low limit set on the amount of memory it can allocate.

This will only work if you're running a 64-bit operating system though.

If that's not the issue, try to post the crash log if you can. If you're using mods and have ModLoader installed, take a look at the modloader.txt file in your .minecraft folder right after a crash. Specifically, the lines near the end of the file. It could shed some light on your problem.

The server could be doing this in a number of ways. It could be using a custom Bukkit plugin, or it could be using a command block sequence.

If you want to do this in your world, you can with command blocks. Put the command execute @e[type=Snowball] ~ ~ ~ summon Fireball ~ ~ ~ on a clock, preferably a fill or setblock clock. Any snowballs in the world, wether thrown or dispensed, will be turned into fireballs. However, this won't apply to dropped items snowballs.