Assuming all goes well (no errors), your Boot Camp installation and third party software should not be touched. What may change is compatibility. Rosetta does not exist in Lion and newer, so PowerPC software will not work without running Snow Leopard Server in a VM, such as Parallels. If your version of Office is 2004, it will also be dead and you'll need to upgrade to Office 2008 or 2011. Or again, run it in a VM. Parallels itself may also need to be upgraded, depending on the version you have. Check on the vendor's site to see which versions of the Mac OS your current copy supports.
Actually one advantage of your situation is that if you have Windows XP installed into Bootcamp, it should survive the upgrade to Mt. Lion. Once upgraded, Bootcamp will not install XP.
Parallels in Mt. Lion requires the last update to version 7, but I recommend Parallels 8 for complete stability with Mt. Lion and additional features including cut & paste and Coherence in Snow Leopard Server, if you have need to use SLS in virtualization (for example, to regain access to Rosetta for PowerPC apps).