The simplest way is to connect to gmail thru your e51 and let t sync your contacts. Then switch phone off, switch on your android phone and use gmaill app. Your contacts will sync into your android.
The harder way is to connect e51 to Nokia PC Suite on your pc. Pc Suite came with the phone and is also available as a free download. Sync your contacts, then tell PC Suite to export the contacts in vcard format. Then login to gmail from your pc. Click contacts and import the file that PC Suite had created. After google has imported your contacts use the gmail app in your android phone to connect to google and your contacts will be auto-synced.