Okay...updated, and it seems to be working!
First, had to delve into the settings a bit. I uploaded a RIP (rescue is possible) CD to the datastore along with one of our XP install disks.
Second, the bootup was impossibly fast. There's a setting to control that, and to control forcing it to go to the BIOS setup at boot, from the edit settings for the VM. Need that to change boot order to work with the CD before the hard disk.
Third, attach CD ROM image from datastore (RIP CD) to the CD drive.
Fourth, remember to "connect at startup" for the CD drive. Whoopsie.
That's how to get it to boot from another source. I booted RIP and had it run Testdisk, which did some repairs to the partition but it kept detecting that the number of heads was misset (I'd change it in the geometry menu but it just wasn't "saving" the new settings...haven't figured that one out.) Reboot, this time it got to the point where it would blue screen. Progress!
Next was a trip to Windows XP's bootable ISO and from there into the recovery console. I ran fixmbr, then fixboot, then chkdsk c: /p twice. Did a quick dir to see if files looked intact (like ntdetect and ntldr) and then exited, shut down the VM and removed the disc from the virtual drive (disconnect at powerup) and crossed fingers.
The VM booted up. YAY!
Thank you to all who offered suggestions!
You can't access USB storage from within ESXi unfortunately so that's not a runner. What you can do is use Veeam FastSCP as an alternative to using either the VI Client or something like the VI-Toolkit which is really just using the same mechanism. External SAS enclosures are an option - you can hot add storage that way. You've already discovered the NAS option.
What sort of copy speed are you seeing? - If nothing else is interfering you should expect to be able to hit 50+Meg/sec over GigE, maybe even a lot more if the NAS target and your source datastores are fast enough. USB would top out at not much better than around 30-40Meg a second so in most cases you would expect GigE to a decent NAS to be faster.
Best Answer
I don't know if this is possible but it seems correct. Just give it a try. If you remove the original VMs instead of deleting them, you can re-register them if it doesn't work. Personally, I would deploy a test VM with HW version 10 and give a try first.
Oh, there's something else you can try: Downgrading the virtual machine hardware version in ESX/ESXi states that you can
However, since this is a new VM it will also have new MAC addresses.