forgot to mention:
OS: Windows XP SP 3
java -version: java version "1.7.0_03"
Java SE Runtime Environment (build 1.7.0_03-b05)
Java HotSpot Client VM (build 22.1-b02, mixed mode, sharing)
Serverstart-Command: java -Xmx1G -Xms1G -jar Tekkit.jar nogui
Server and Client Version: newest: Launcher EXE (0.5.4.9); Tekkit 2.1.1