Good decision to go away from evil pic empire and support arduino 
I have made an automated installer so maybe your transition your can go smooth:
http://arduino.cc/forum/index.php/topic,118440.0.html
If your XP is up to date you will only require to double click the installer otherwise, you may need to install the framework 4.0 from windows update (not for arduino but for some small enhancements I added to the ide)