if your pc is running fine speed wise apart from wehn you are online, then you can limit the problems to browser or internet connection.
Since you have tried a differentbrowser that rules that out.
if you want a registry cleaner, use ccleaner, it is free and will repair problems for free, aswell as remove any unwanted temporary files you dont need which will help the general performance, but if the problem is your connection that will still remain.
there are some commands you can use to try and clear some issues with this, but it may be something beyond your contriol, i.e. your isp.
if you dont know enough to check these yourself, you could always pm someone here in the know and try to get a netmeeting set up, this will let them have a look and rule most things out, or at least give you an idea of what may be the problem, make sure its someone you trust tho, as they will have a fair amount of access to your pc.
I wouldn't go round in circles trying reg cleaners, if you've a virus or the such they wont help, and if its a reg issue your likely to have slow performance full stop.