Mac Forums

I just had my macbook this february 2010 and now it seems to be running slow. My friends says i dont need any anti virus for this. But is there any program or software that i can download for free to clean up my computer? Like Ccleaner for windows. This is my first time to have a mac that's why im not yet used to it. Before when i open the power button and it loads up real fast. Plus when i use my other programs like yahoo messenger and mozilla it runs fast too. Now it takes up for about 7minutes to load up. What should i do? Hope you guys could help. Thanks :-)