I used a SCSI PCI card which I got at the same time as the hard drive (I think I already said this in the first post). I used a useful hard drive imaging utility called "HDD RawCopy" (or something like that) to create a raw image of the drive under Windows. I then used a Macintosh emulator called SoftMac (it's the only one I can find that will emulate a raw hard disk image as a SCSI drive; Basilisk II just makes at a "disk drive") to format the disk image and install the basic system software. I then wrote the prepared disk image back onto the hard disk.
I still use pretty much the same procedure for any serious reformatting or reinstalling procedures (and I still make images the same way for backup purposes), but I now also use Linux to copy a few files onto or off of the hard drive, since I have installed the required packages to allow native support for hfs volumes. Basilisk II on Linux will also allow me to select the SCSI device as a SCSI device in the emulator.
By the way, the guy never sent me the external enclosure, so unfortunately it's still a bit of a job to connect the drive to the PC. I have to disassemble both the Mac and the PC every time I want to copy just the odd file here and there. I usually keep a collection of files and then, when there are enough (or when my next backup is due), I copy them across.