I had very similar problems using DDS3 DAT drives with a Adaptec SlimSCSI 1460D adaptor under SuSE-Linux 6.2. I could read tapes, but when I tried to write, the system freezed earlier or later
In my case the reason was, that the system seemed to lack tape-support, although the kernel was compiled with built-in tape-support. It helped to load the st-module before the device driver module (in my case aha152x_cs) by modifying the file /etc/pcmcia/config:
device "aha152x_cs" class "scsi" module "scsi/st", "aha152x_cs"
(see also the PCMCIA-Howto section 4.5 "PCMCIA SCSI adapters").
Probably this helps you, too.