I'm not sure this will works, try it.
function drawWindow()
gui = {}
gui["_root"] = guiCreateWindow(left, top, windowWidth, windowHeight, "Login/Register", false)
gui["tabWidget"] = guiCreateTabPanel(0, 20, 251, 181, false, gui["_root"])
gui["tab_2"] = guiCreateTab("Register", gui["tabWidget"])
gui["registerUsernameEdit"] = guiCreateEdit(110, 10, 113, 20, "", false, gui["tab_2"])
guiEditSetMaxLength(gui["registerUsernameEdit"], 32767)
gui["registerPasswordEdit"] = guiCreateEdit(110, 40, 113, 20, "", false, gui["tab_2"])
guiEditSetMaxLength(gui["registerPasswordEdit"], 32767)
gui["registerPasswordEditRepeat"] = guiCreateEdit(110, 70, 113, 20, "", false, gui["tab_2"])
guiEditSetMaxLength(gui["lineEdit"], 32767)
gui["registerButton"] = guiCreateButton(52,105, 131, 23, "Register", false, gui["tab_2"])
end
addEventHandler("onClientResourceStart",getRootElement(),drawWindow)
addEventHandler("onClientGuiClick", gui["registerButton"],
function on_registerButton_clicked()
username = guiGetText(gui["registerUsernameEdit"])
pw = guiGetText(gui["registerPasswordEdit"])
pw2 = guiGetText(gui["registerPasswordEditRepeat"])
outputChatBox(username)
outputChatBox(pw)
outputChatBox(pw2)
end
)