I dnt think it is possible...
Actually celldweller he must be having WinXP or later OS in older HDD. The data he is talking about could be encrypted or he must be using password enabled account thus all the items under My Documents etc. are encrypted. I do not think it is possible to access them...
I was in such situation once. All I did was, boot the system with older HDD and copied all the data to normal folder location e.g. C:\OldData. Switched Primary/Secondary HDD and re-booted system normally with OS in new HDD. I was able to access data in OldData folder.