Legal Notice/ Banner Text

I need to have a legal notice show up everytime my users logon to the network. I know i have to use a group policy to apply it to the whole domain by doing the following: click Start, click Run and type Gpedit.msc. Click OK.
Click the + next to Computer Configuration, then Windows Settings, then Security Settings, and then Local Policies to expand these folders. My problem is that i do not have enough space to type in the Message Text for Users Attempting to log on. Is there anywher i can place my legal notice text? Please help