How Do I Write Polite Emails to Senior Staff for Permissions and Requests?

I'm an employee of a reputed health group. I joined here as an HR Executive, and my job profile includes recruitment and training and development. I request you to provide me with some examples for writing emails to higher officials or requesting favors. For instance, if I need permission to attend training classes tomorrow at 10:30 am, to different HODs, or to get permission to use the conference hall on 18.10.2010 at 2:30 pm, how should I draft the email?

Please help.

Regards,
Rajlaxmi