neither ambrose_1.
just the entire contents of the drive into a directory say, 'old_pc' then take the old drive out(that way you wont have to worry about getting into the case again)
after that copy the files you want over that you know you want, bearing in mind that mouse-dragging them within the same drive constitutes a move, not a copy. as far as the programs go, you'd best reinstall them on the new pc, unless you know that you dont have to.
the files and progs you can copy over just fine.. however if they're windows apps that need registry settings then a re-install of that application will be in order..
as far as conflicts because of OS's goes, the way most operating systems work is they write a little bit of data on the first hard drive when they install(the first HD would be C drive. which will be the one with XP on it) saying what OS to load, or what OS's exist and where, and/or other info for a multi OS boot menu..
installing a second hard drive, you wont be able to boot from it unless you add a line into the 'boot.ini' file to look to the second HDD aswell, and thus give you a choice. the thing is, the second hard drive will be D drive, and every reference to a file using C:\ will be wrong. so it wont work anyway.