I dropped the .jar file into the plugins folder and ran the server console and it produces this error:

2011-10-05 22:03:02 [SEVERE] Could not load 'plugins\OpenWarp-1.1.jar' in folder 'plugins':
java.lang.NoClassDefFoundError: com/pneumaticraft/commandhandler/PermissionsInterface
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:168)
at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:215)
at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:136)
at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:139)
at org.bukkit.craftbukkit.CraftServer.(CraftServer.java:104)
at net.minecraft.server.ServerConfigurationManager.(ServerConfigurationManager.java:52)
at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:136)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:348)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)
Caused by: java.lang.ClassNotFoundException: com.pneumaticraft.commandhandler.PermissionsInterface
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:36)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:24)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 11 more

MC: 1.8.1
CB: 1240
OW: 1.1

This is a known issue - I hope to have a fix by the weekend.

@Undearius: should be fixed in build 115 and newer.