Your second option woyuld be best if your running windows XP. If you take your current harddrive and connect it to a different system, windows XP will detect it and will not boot because it thinks the HDD is stolen. (all a load of balls about privacy policies i guess). This is when windows XP really does get too smart for its own good.
The only way you would be able to get your data back after selling your current system would be to get a brand new HDD, install windows on it, boot from the new HDD, connect the old HDD as a slave and then copy the files over to it.