My Mac is moving slow

I have a MacBook that's about 3 years old. When I originally purchased it the OS was Mac OS X Tiger. I recently upgraded to OS X Leopard and ever since it has been running rather slow. I have pasted my specs below. Will updating the RAM to 2GB help or do I need to update the harddrive?? If updated the RAM to 2GB will help, is there any that you can recommend and possibly a website to purchase it from?

Thank you

Hardware Overview:

Model Name: MacBook
Model Identifier: MacBook1,1
Processor Name: Intel Core Duo
Processor Speed: 2 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 2 MB
Memory: 512 MB
Bus Speed: 667 MHz
Boot ROM Version: MB11.0061.B03
SMC Version: 1.4f12