Scheduling an Apex Job through the ui

Setup -> Develop -> Classes

You will see a "Schedule Apex" button. You can set up the timing from there.

Just checked - there is a Schedule Apex Button on the Setup > Develop > Classes screen, although I struggled to find a mention of it in the Scheduled Apex doc.

Step 1: Implement the Schedulable interface in an Apex class that instantiates the class you want to schedule. Step 2: From Setup, click Develop | Apex Classes and click Schedule Apex.

for more information pls refer: https://help.salesforce.com/HTViewHelpDoc?id=code_schedule_batch_apex.htm&language=en_US