A lot of newer IDE devices cause the access light to stay on. The same thing happens for me with both a 20GB Samsung hard drive and a CF adapter. If the system boots from the drive, it's working!
An 8GB card should work from a hardware perspective, but a stock 3.1 system won't be able to partition/format it correctly. Patches to scsi.device and FFS are required (although since you are using PFS the FFS issue is not applicable), and a different partitioning program is needed. These issues are also not relevant if you are using 3.5 or higher, except your boot partition needs to be within the first 4GB of the drive.
