How'd you install the drivers if you can't boot to the disk? Or if it won't read the XP disk it could be you have a problem there, unlikely though if that's the disk you used to load XP.
NTLDR is missing is basically your computer saying I don't know where to boot. Usually this is associated with a hard drive that isn't partitioned or formatted. It could be that something didn't install correctly on the boot sector as well. Also your ram or motherboard, but it's unlikely.
My advice is to check the disk, try to boot it from another computer. If it doesn't work you need to fix your boot sector, which usually means a format, but there could be another way. . .
