This is what I did to get it to work on CM 6.1.2 on Moto Droid 1.
1. Buy and install Root Explorer.
2. Download the Vending.apk, version 2.2.7, and put it at the root of my SD card. Do this via dropbox or the USB cable. It doesn't matter where you put it on the SD card or how you get it there. I downloaded an unsigned copy of 2.2.7, I think. Maybe it doesn't matter. Here's a link to the signed copy:
MEGAUPLOAD - The leading online storage and file delivery service
3. I then downloaded/installed ZipSigner from the Market:
https://market.android.com/details?id=kellinwood.zipsigner
Yes, I realize you need a working version of Market to get this APK. But you can get this app with Market 1.8.x.
4. I then run ZipSigner on the new Version.apk that you put on your SD Card. This should take a few seconds. You should see it crunching away via a status bar.
5. Back up a copy of your current Vending.apk (version 1.8.2). Just COPY it to your SDCard, and change the name to "Vending.apkOLD" for example. Just don't replace your new copy that's sitting there.
6. Using Root Explorer, copy your new Vending.apk, which has been signed by ZipSigner, from the SD card to /system/app/Vending.apk
This will effectively replace your Market app. What worked for me was writing over the existing app with this new one. Don't ask me why.
7. Using Root Explorer again, I changed the permissions of the Vending.apk to what they're supposed to be:
Vendingapk permissions image by gtpdjw on Photobucket
And that's it. I rebooted right away. I held my breath, and it worked.