If your PC seems sluggish, use RESMON to uncover the bottleneck.
Click Start, type RESMON and press Enter to launch the Resource Monitor. Click the CPU, Memory, Disk or Network tabs. Windows 7 will immediately show which processes are consuming the most system resources.
The CPU view is particularly useful, and provides something like a more powerful version of Task Manager. For example, if a program has locked up, right-click its name in the list and select Analyze Process. Windows will then try to tell you why it's hanging (the program might be waiting for another process) which could give you the information you need to fix the problem.
Resource monitor keeps a careful eye on exactly how your PC is being used.