A new drive would not be automatically seen, and it certainly wouldn't mount into the linux file structure on its own.
The "simplest" thing to do might be to plug the new drive into the slave cable for IDE. Then edit your /etc/fstab, and set something like
/dev/hdb1 /data reiserfs defaults 0 1
Then you could set up vsftp or apache to use that directory (/data) as its local root, and give everyone read/write permissions.
Other possibilities include making the new drive your /home partition, which takes a little bit more work, but isn't too bad. Google or look here for how to move /home from one disk to another. Also if you're going to do that, make sure you have knoppix or some other live distro around, so you can save things if they get screwed up.