My father is looking to purchase his first iMac, but wants to be able to dual-boot into Windows XP to allow him to gradually get used to the new OS. I know that Windows XP is not "officially" supported in the latest version of Boot Camp, but I have seen posts elsewhere that say it is possible to install it. My concern is with drivers. Are there appropriate drivers available for Windows XP and the newer iMacs? Will he have any real issues with this setup? I'd love to hear any advice you have.
Are there appropriate drivers available for Windows XP and the newer iMacs?
Since the newest incarnation of Boot Camp (that is, version 5) only supports Windows 8 and Windows 7, both 64-bit, there are no official, supported drivers from Apple. You may find matching drivers for the basic stuff, but I'm afraid that setting up the iSight camera, sound or even WiFi/Bluetooth won't be a piece of cake.
If you want to try your luck, though, peruse this post. It applies to Windows XP on a iMac (early 2011), but contains useful information, for instance, the recommendation to use Windows XP SP3 media.
Check this link http://egaille.free.fr/imac27/ too. It includes drivers for an iMac (early 2011), you may be able to reuse some.
Will he have any real issues with this setup?
In your situation, I think it is quite a bad idea to install Windows XP.
Apple is very clear on what is supported. Even if you get Windows XP to boot, missing or unstable drivers are a pain, some functionality may be missing and your father will blame the Mac, although other solutions (I'm thinking of a VM) will run just fine.
That's a pretty bad start for a newcomer to the Mac world: a potentially incomplete Windows installation and an entirely new OS to learn.
Boot Camp vs. virtualization
I already put this in a comment, and I know your father was less than thrilled with the idea, but let me repeat it here:
Instead of Boot Camp you could virtualize Windows XP with Virtual Box, Parallels or VMware Fusion. Your father could run Windows XP full screen and OS X apps side by side and easily switch between them. Moreover, he could go back anytime without annoying reboots to the familiar Windows interface while getting increasingly used to OS X.
To make it as painless as possible you could turn automatic login on in System Preferences>Users & Groups>Login Options, add your virtualization solution to Login Items and configure it to start the Windows XP VM when opened, for example, in VMware Fusion: