Mac software is totally different to Windows software. The software is written for the operating system: Macs run Mac OS X, and not windows.
So, you will have to use different software, or at least different versions of the same software. For example, there is a Firefox for the Mac (I'm using it now), totally the same as the Windows version. There's a version of Microsoft Office for the Mac too, but its not the same exact one as Windows. Same goes for most other major programs. Others are replaced by equally good, other software (many supplied by Apple as default).
What software do you use?
The only major thing to do is find out if any software you use is Windows-only. If so, you may be in trouble.
XT format: what files are these? I've never heard of the XT format.
(Having said all of the above, you have two options for Windows software. First, you can install Windows on the laptop too, to boot into instead of Mac OS X as and when you want to. However, all the security concerns that come with Windows still exist -- the Mac hardware isn't any more secure than any other hardware. Secondly, you can buy virtualisation software such as Parallels, which makes Windows software run together with the other Mac OS X programs. However, it doesn't run perfectly, and detracts from the integrated interface, making the programs appear alien.)