Doing what cryptodan suggested will present a full list of processes running on your system, but the process name alone often isn't enough to determine whether a process is malicious or not - you need to examine what's hooked, or "running under" each process.
To do so, download Process Explorer from:http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx
Executables (.exe's) aren't the only malicious files that can run on your system. While I don't yet understand the technical details, I've been told that .exe's and .dll's only differ by one bit (and both are capable of malicious activity). Process Explorer is useful because you can compare file paths, file names, parent processes, and digital signature validation to help determine if a particular file may be nasty.
1.) Start > run > msconfig
2.) Make sure that, under the 'General' tab, 'Normal Startup' is selected.
3.) Open Process Explorer.
4.) Under the Options menu, enable 'Verify Image Signatures'. An internet connection is required for signature validation.
5.) Under the View menu, enable the 'DLLs' 'Lower Pane View'
6.) Process Explorer presents a list of each running process on your system, along with the DLLs and other files they depend on/load with. Sorting the lower pane by company name is incredibly useful for quickly spotting suspicious files.
You can use a search engine to search for the filenames of any suspicious files you may find, but PLEASE BE WARNED that the internet is loaded with false information, and deleting one or more files you see in Process Explorer can render your PC inoperable. If you have reason to believe your PC is infected, get with a Malware Response Team member who is specially trained to determine what's nasty on your system and what's not.