Hi,
The ASA doesnt really support this officially. The only thing supported officially is configuring an ISP Failover when other or the ISPs fail.
To achieve somekind of load balancing you will simply either have to route half of IPv4 address space towards one ISP and the other half towards the other ISP.
Other than that the solution might be to use the NAT configurations on a 8.4 - 9.1 (maybe even 8.3) software level to manipulate where certain LAN networks traffic is forwared to.
But we dont really have any information based on your above post as you dont mention software level.
- Jouni