Vista X64 and XP X32 Dual Boot Driver Question

no, they wont "conflict" - they won't be running concurrently.

you will install all software - apps and drivers - in each OS.

also, if you normally maintain a 'program files' folder on another drive (say, drive D for nonessential software (as opposed to installing it on the system drive) then you'll need to have separate locations for them for each OS as well. in such a case, you would end up on D: with a "program files" for XP32, and a completely separate "program files" folder for V64. In addition, when you install 32-bit apps under V64, you'll also end up with a "program files (x86)" folder [that is the actual name, as you'll see when you start installing 32-bit software). Because of the 'program files' folder name conflict, you'll have to either:
- manage software installations on D: carefully (a problematic PITA)
- or use a different name for 'program files' on D: for one of the OSs (a problematic PITA)
- or mount different partitions as 'program files' for each OS (doable)
- or mount different partitions as D: for each OS (the safest method).
if you do this mounting-dance, it is generally best not to even mount the "D" partition from the "other" OS at all... altho it can be handy to mount it in a folder just so you can access it to copy files or whatever. for example, i keep a C:\_MNT\ directory that contains mountpoints for partitions that are 'officially' part of a different boot but which i want to be able to get to if i need to. having such a "mount directory" on C: ensures that its contents change depending upon what OS you boot. This scheme is also handy for keeping partitions where you store backups handy without using up a drive letter.

if you install everything on your boot drive, then that whole mess won't be an issue of course.

In addition, it can be very handy to use the same SID for both OSs, to make the setting of file permissions easier if you'll be accessing files from the "other" OS. If you do that, you'll also want to ensure that your user SID is the same for both as well. the first user (after inital administrator) for XP appears to get a SID ending in -0003, but for V64 the first one apparently gets -0000, so, for example, under V64, you'd add 3 users (one admin created during install, and 2 dummys) before adding your 'real' user so that they both end in -0003; the dummy accounts can then be deleted. It is possible that optional components may create one or more users during their setup - altho i didn't have it happen to me on Vista as it did on XP, but watch out for that... if you add too many and pass the SID you were trying for, you get to reinstall (there's no proper way to decrement the counter).