The AMD 64 Athlon/Opteron and Intel Itanium2 are backwards compatible with 32-bit so their should not be an issue with mixed bit dual boot configurations. Dual boot is great for testing various distros but I never really found it practical. If you so choose you can install both WinXP 64-bit/32-bit with a dual boot of SuSE Pro 9.1 or what ever distro you want.
I still see the Novell deal for SuSE 9.1 the best offer when comparing to other Linux distros and even what Microsoft has to offer. The great thing for not only studios but also freelance artists is with SuSE Pro 9.1 you get both 32-bit and 64-bit install discs. This means you can take your time upgrading your system/network. The cost of SuSE Pro 9.1 beats what other developers are currently offering since at present only Novell is offering two OS in one retail box. Even if you were only getting the 64-bit OS which is still backwards compatible you are getting a good deal for the cost.
Since SuSE Pro comes with server capabilities you can opt to install it designating one machine as server and the rest as clients. Doing this still only cost you the purchase of the one retail box since you are allowed to freely distribute across your network.
Note under the current license agreement for Novell/SuSE you cannot burn copies of SuSE and sell them. You can make copies and give them away for free under the GNU/GPL license (ie: install on a friends PC) or sell the original boxed set with all materials included. The 90 days Tech Support only applies to the original purchase though a new user can purchase one of the many maintenance support packages through Novell/SuSE. See link for better understanding.
http://www.suse.com/us/private/support/licenses/http://www.suse.com/us/private/support/licenses/
Sorry for the long winded post but I'm excited waiting in anticipation for this release. 