Firstly, there are a few NT USB drivers available and they do seem to work.
Drop me an email and I'll dig one out for you if you want to try it. So
far it's been well tested on Dell Latitude systems and seems perfectly okay
with zip drives, memory sticks and all-in-one printers. Cameras should be
okay as well as they work as mass-storage devices, the same as USB memory
For dual-booting with XP, you need at least Service Pack 4(IIRC) and
preferably SP6a. Next, you need a good 1.5GB of space on an uncompressed
drive. Install XP in a separate directory to NT. My personal preference
here would be to reduce the size of your NT partition with the partition
manager of your choice, create a new partition and install XP in that.
Just remember that *most* programs installed on one OS will need to be
installed on the other if you want to use them both with NT and XP.
 Insert all the usual "FFS, Backup first!" disclaimers here