I had the exact same problem until I downloaded Sims2Pack Clean Installer. You can get it here, http://sims2pack.modthesims2.com/
. You run the program and search for the files by using the browse option. It then should then be able to turn the SIMSLSPACK files into compatable package files for the game. However, even after I did this not all of the files that came with the welcome pack installed. I'm not sure why, hopefully someone who knows more about this kind of stuff can help you out.