They supposedly were processing my order yesterday but I haven't got an e-mail confirmation, it will be interesting to see what shows up on my doorstep next week!
I suspect someone screwed up that web order page ...
If you take the $389 and add $299 you get $688 (after rebate etc)
On their site you can order a 1600SC - bigger box, dual-processor motherboard - with a 2.4 GHz Xeon (SMP capable) with onboard SCSI and the 36 GB 10K disk for $699 (after rebate etc) which would be a better deal than the "you have to buy a $299 SCSI card!" rip and a non-dual motherboard.
And that page only shows $199 for a separate SCSI card *and* makes clear that "embedded SCSI" is the no-cost option.
Something's screwed up at Dell ...