I am using Windows XP - SP2. How can I check how many processors are available in my system and how many cores in each?
From the command line you can use WMIC:
For a multi-processor setup you should get one result line per CPU.
If you already have Powershell downloaded, you can execute the following.
Then look at NumberOfCores NumberOfLogicalProcessors values. It uses Windows Management Instrumentation just as Joey's does, but you have more options in what you do with the info over the Windows Management Instrumentation Command-line (WMIC). For example you can add
More info about Powershell and WMI can be found here