If everything is running well I wouldn't bother with Win 7. General feedback so far for Win 7 has been positive and I would agree with that - as I have be using the Release Candidate on my laptop.
But since everything is working well on your computer - I would suggest that it wouldn't be worth the trouble.
If you do decide to give it a try - you should install it on your first drive (Windows does not like being installed on a second drive - as it gets a bit confused). It makes sense to leave your second partition alone regardless - since it has all your data on.
If you look through the Windows 7 forum you will find a guide on how to set up a dual boot system - so that when you switch on your computer you will get a menu to choose whether to start XP or Win 7.