Well I would avoid the mixed editions they tend to contain hidden trojans etc.
Rather get the untouched IMAGE from the MS site and then use an MSDN key to unlock it.
I recomend Vista Ultimate x64 Edtion.
Xtreame
PS. In theory you could use Poweriso to rebuild the image on two disc and still have it bootable. When the read error occurs just swap discs, you might hoever end up swapping back and forth allot, you could also convert the image to install off a flash drive.
Or just buy an 8gig dvd they are cheap enough