Any MS Office programs will need to be reinstalled, so that the W7 registry knows where the program lives. Any program that had data written to the XP registry will need to be ri installed unfortunately.
Do you really need to dump XP?? It will continue to operate as well as it does on the day support is stopped. Those who write programs to exploit vulnerabilities, will be targetting W7/8/9(?) and no doubt forget XP exisits.
Those businesses that continue to use XP, will probably do so, due to the difficulty in migrating their systems to newer platforms.