How to achieve automatic roaming between two Cisco Aironet access points?

I have two Cisco Aironet 1141 access points covering an office; the access points are configured identically (each of them with two SIDs) and are fully working; they are standalone access points, not centrally managed ones.

When a client devices moves between them, there is no automatic handover of the connection. It needs to be re-established again.

How can I achieve client roaming between the two access points?
Can this be achieved without a central management server/controller?

Client roaming should work just fine... in theory. Just double-check and make sure the SSIDs, passwords, and authentication types are identical on each AP. Is the issue occuring on all clients, or have you only tested one so far? Perhaps that client needs updated network drivers.