Siggys hydronic know how 2

I recently purchased Johns Hydronics Know How 2. I am having trouble installing it on a HP computer running XP. Actually I have 2 HPs and I get the same failure on both. I then installed it on my daughters laptop which is running Vista and had no problems. I talked to John about this and he sent me another copy and offered a refund but so far I havent been able to figure this out. I told John it was time I upgraded to Vista anyway but now I see Windows 7 is coming out next month. So I figure I will wait even though they are offering the free upgrade if you buy the computer now, I would rather buy the computer preloaded. So here I am with XP for another month and this disk here that I would love to review. Question is... Has anyone else had this problem and found the fix?