He ALREADY has a legal copy of windows, on his new PC. His old HDD has th epirated copy, and now he's afraid that the pirated copy may corrupt his new and LEGAL copy of windows 7.
There is no problem with that, you can just transfer the old files from your old HDD, it will cause no problems.
That was not entirely clear.
"im currently using original windows 7 home premium"
But sure. If the old stuff exists on a different drive....connect, pull off the old data, and wipe as necessary.