Google Jowie and apply the tweak from his blog!
Here I just copy the relevant bits:
With all that information in hand, I went about recreating the .iso file to burn back to disk to see if simply setting checking the option in imgburn to not use the versioning scheme worked.
First thing you will want to do is extract the boot image off of the DVD created from the .iso downloaded from the beta site, you can access this while in "Build" mode.
While that DVD you burned is still in the drive, and after you've extracted the boot image somewhere to your hard drive, click the button to browse for a folder to add the files from the DVD to the image. Just add the root of the drive, you should then have something that looks like this.
On the Options tab, ensure the file system is selected as ISO9660 + UDF, and the UDF version is set to 1.02. These settings matched what the MS .iso file were set at, and is the only reason I chose them. Other settings may work, experiment if you like, rewritable DVDs are your friends.
Now we get to the part where we configure the ISO9660 settings, on the Advanced tab, Restrictions subtab, then ISO9660 subtab, I set the Folder/File Name Length to Level X, and checked all the options toward the bottom of that pane.
We're almost done, onward to the Bootable Disk tab. Check the option to make the image bootable, select None for emulation type, browse to the boot .ima file you extracted earlier, and set the sectors to load to 4(8 if you're building a Win7 DVD!).
That should do it! Create the new .iso file and then burn it to disk.
