If you are using an Cisco Autonomous AP you can use the local Radius embedded in the AP an USE CCMK (with EAP-FAST for example) and WDS to manage CCKM under this infrastructure.
If not, normaly the lighter encryption ciphers gets the lower latency in roam.
The most important question : what is the security setting on your SSID if you don't have ACS ? Do you still have 802.1x authentication ?
If you have wep with a static key, then there is not much needed for fast roaming.
Wep with 802.1x would require a WDS to be set up.
But for a wep static key, the only thing you need is to have the different APs connected to the same network and putting the clients in the same subnet, have the same SSID name and same security settings.
Hope this helps,
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