First of all, a 40 GB drive is WAY overkill for any Atari, especially an ST or STe.
I have a 2 Gig on mine and it still has plenty of room even with all the crap I have on it.
Second of all... there is an IDE interface out there. Paskud makes an IDE interface that plugs into the cartridge port. You could also do what I'm planning on which is to get a SCSI to IDE Adapter. See EBay -> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=5127984932&ssPageName=STRK:MEWN:IT
Good luck to you in whatever you decide to do...
Atarian since 1980
STs: 1040STfm, Falcon 030 w/ 14MB, 10GB internal HD and BlowUp graphics adapter
8bits: 800XL w/ 32-in-1 OS and Supervideo 2.1 Upgrade, Happy 1050, APE (Registered), Commodore 1702 Monitor and PC storage unit
Wish list: MegaSTE, 130XE, 65XEGS