MSCONFIG the OS (if Windows) and ditch all those pointless proggies that are probably starting up. xD Painfully common how many people have this problem. Also, go through your services, and ditch the ones you know you don't need. Low RAM is a common cause of slow loading and a tale tell sign is when parts of windows load but others don't until later.
There are heaps of things you can do, within a Windows OS. (can't speak for others, as I only use Windows) There's services, cleaning the registry, defragging, tweaking the pagefile, tweaking cache settings, etc. Since what you're asking has little or nothing to do with hardware: "I want to speed up my OS." is basically what you're saying. Post in the software forum, to ensure you get the right support. Might also help to know whether it's RAM or your CPU that's letting you down, as there are steps that can partly make up for either of these drawbacks.
G'luck.