Problem with World Edit Comments and grafics ingame

Good morning,
I've got problems with minecraft worldedit comments.
1st: I can't get a compass with the comment: /item compass 1 (unkonown command) But I have seen the comment in you tube. Why do it not work ?
2nd: If I am marking two positions for building a great area with blocks, i can't see the blocks after typing: //set 1
Sometimes I can see a little bit of blocks, but not all. The rest is not there or it's a invisable wall. I can't going throught the invissable wall.
I must leave the game. After new logging in I can see the new blocks!
Can it be a Problem with the RAM????
If have got a Bukkit Server on my computer.
Windows 7 (32 Bit), 4 GB RAM, nVidia GeForce GTX 275.
In Game 1024mRAM on Bukkit Server.
How can I raise the RAM on my Server? I have searched for answers in google, but I haven found something!
I hope someone can help me.
i'm sorry for my english
have a nice day
greetings
ArmaSteiner