Difficult Upgrade from Cubase Studio 4 to full Cubase 5

My PC processor is a AMD 64 3500.
Since I have upgraded from Cubase Studio 4 to full Cubase 5, I can no longer do music properly. In order to avoid craking/poping sounds I need to increase the latency to a point I cannot record any more. Is it because my processor is not powerfull enough?

If I could use Cubase Studio 4 to record and Cubase 5 to do some track editing and mixing I would be quite happy (I hope). But when I installed Cubase 5 I lost access to Cubase Studio 4. Is there any solution to this problem that is a bit discouraging :cry: