When a program installs, invariably, it writes certain information to the registry. You can't therefore, just copy the program files and expect them to work. They wont. You need to reinstall the programs from their original CD's and confirm they will work in XP.
As far as data files are concerned, there shouldn't be a problem with them, providing you have the appropriate program in XP to open them. They should however copy across without any problem. If they are program dependent, for example data files for something like Quicken, you must install the program first, and then import the files into the program.
Is this what you meant?