Several... either install a HomeScreen replacement (Home++, SweeterHome ect.) or you can install the 2.1 Launcher (the default launcher from 2.1 that's been pulled and ported to run on 2.0.1 ROMs).
The Droid will notify you when there is an update. Right now, there is a app called "Launcher (beta)" but it also is buggy. Wait for 2.1, we should be getting it some time this month. If it doesn't come with 5 home screens, then use the 3rd party app. Anywho..yeah, the droid WILL let you know when it is ready to update. It will be pushed OTA (Over The Air) from Verizon to your phone.
If the update doesnt come with 5 screens the guys at Android Central say they will have an APK for the 5 screens that is not buggy since it will be running a 2.1 app on 2.1. That's why it's buggy now running on 2.01.
I spent all day yesterday trying to find a good one, but I had no luck. I used Panda, Home++, Launcher+, OpenHome, and a few others and they were all buggy and caused forced closes. I finally gave up, and will just deal with the stock until 2.1
For the record, Home++ was the least buggy of the group.