Is it just with the SKY HD box that you are using as a source? I havent seen this problem with the PS3 or Sat HD box we have here. (will have a look into it though)
When recording are you leaving the bit rate as standard? As thats going to give you about an 8gb file. I havent found any software that cuts the size down to a single layer DVD and still retain the quality. Only option would be to convert to AVI etc.
Which version of Nero have you got? As im sure the one i have didnt give me any out of sync problems. <will be Nero 9>