Hello Peter
First,you've got quite a few programs open, so
(1) why are you running ZoneAlarm? Vista's firewall is probably as good.
(2) Why are you using two browsers (Firefox & Explorer)?
I'm at work, so this is from memory, but with Vista there is a good tool for looking at the resources that are being used at any time. To get to it, press Ctrl/Alt/Del and the use the option to start the Task Manager. Task Manager's Performance tab will show you your processor and memory usage, but for more information, on the Performance tab, press the Resource Monitor button. This will give you a much more detailed set of information about your PC.
The usual reason I find for slow PCs, is lack of memory, so that switching between programs involves Windows doing a lot of disk accesses to the swapfile. You should be able to see this with the resource monitor.
The other reason for slow startuip/shutdown is the number of processes that are running behind the scenes. You can see a list of these in Task Manager, and Googling them will give you more information about what each one does. Antivirus scans that run at startup tend to cause slow running initially, but other stuff like indexing software and multimedia managers also can have quite an impact. Use task manager to see what proceses are running, and click on the CPU column to see which ones are using most cpu resource.
Hope that helps
David.