Sometimes older games like Sim Safari cause problems with WinXP.
Microsoft has a solution here http://support.microsoft.com/default...b;en-us;324767
I don't know how experienced you are with PCs, so if it looks too complicated, just post back and we'll try and simplify it for you.
Basically, what you need to do is get a working copy of the AUTOEXEC.NT file and put it in your C:/Windows/System 32 folder.
Alternatively, there's a small program that does all the hard work for you.
Go here http://www.visualtour.com/downloads
and scroll down to XP_FIX.EXE