Private Servers monitoring

I’m one of the cheapo’s using the 150/150 VPS, I have to have vps for one little website because I need a process that can last while it downloads some files every night. Well, I use almost 0 of my bandwidth or space, yet I’ve now seen my memory/cpu or something spike to 150 once. How can I start to figure out what happened during that spike?

We need some tools as VPS admins to see what is happening when the memory or cpu spikes. I assume it’ll just show apache as using said amount of memory but can we get a better view of the memory usage so we know exactly when it happened and can look through apache logs(are these available for us?).