I'm not sure if there's a standard layout for these things, but there are some key pieces of information which should be included, in order to avoid any problems:
1. Details of the event which is being sponsored. Its title, time, location.
2. The exact amount of money which is being given.
3. When will the money be handed over. Do you need the money in advance?
4. What does the sponsor get in return? Are you printing their logo on paperwork/backdrops? If so, where will it be shown? Who provides the logo? Are you inviting the sponsor to speak at the event? If so, when and how long is the speech?
5. If there are more than one sponsors, who are the other sponsors and are they given equal prominence?
6. Will you be giving the sponsor some pre- or post-event publicity? If so, it's worth saying what publicity you're going to do, just so that they don't expect more.
7. Would you like the sponsor to attend the event? How many guests? Will food be served? Will you reserve spaces for them at the meal?
It really is worth making sure everyone knows the deal when you're dealing with sponsorship of an event. It keeps everyone happy.
If you want any further advice, just say.