The Dani driver referenced earlier supports many older SATA chipsets. I'd try that next.
During install, you will get a chance to use fdisk or the LVM manager with Warp v4.52 to partition the disk. Only use OS/2 tools to do the partitioning, so if you were also going to install Linux or Windows along side OS/2, partition from OS/2 and then install to the existing partition.