Hi there! Old roots can be trimmed. They will be squishy, or hallow. A good root is firm, whitish, sometimes turns green in response to water--DON'T cut it...it's still feeding the plant.
If you're ready to pot, soak the potting medium in water...usually over night...this helps get the bark ready to hold the right amount of moisture and helps reduce shocking your orchid.
If you don't have time to soak overnight, I've heard boiling the medium in water helps speed up the process...just make sure it's cooled off when you go to use it! (cooked orchid anyone? yikes!)
On a side note, if this is a continued conversation from another thread you posted, I didn't see it yet. I'm sorry! Sometimes it's good if it's still from the same conversation, to go ahead and update on the same thread so previous watchers can see your progress easier.