I've managed to import a private key, but how to import an entire wallet?
The best way to switch to Electrum is to send all the bitcoins you have on your old wallet to one of the addresses on your Electrum wallet. This way you'll have all your bitcoins secured with your seed.
- Select "Wallet Properties".
- Select "Backup This Wallet".
- Select "See Other Backup Options".
- Select "Export Key List".
- Select "Omit spaces in key data".
- The important string is the PrivBase58 for every bitcoin address. It is the private key of this address encoded in base58 (encoded not encrypted), which is the (only?) format Electrum accepts when importing.
- Select File → New Wallet
- Enter the private keys you took from armory into the textbox