Hi JoanN,
It wouldn't be possible to create a new Lead and associated Activity at the exact same time, since the Lead first needs to be created before an Activity can be created for and linked to it. However, if you're on the New Lead screen and click the Save & Edit button when you're done filling out the Lead's information, it should take you directly to the Edit Lead screen where you can add an Activity quickly from there. This way you don't have to go to the Leads and Contacts List screen and find the new Lead manually, you can just get straight to editing and adding Activities.
Hope this helps.
- Justin