Software to read voltages

Buy a DVM with computer software.

I've bought 2 from Radio shack, may not have. The first one I rewrote the software. The 2nd one worked with XP, But have not tried under Windows 7.

Do a google search for "DVM with computer software" May need to spell out DVM.
Example:
http://www.multimeterwarehouse.com/MS8220f.htm

Most will use a RS232 serial port connection which means most newer PC will need a USB -> Serial Port Adaptor (Approx $15 -> $20).

If lucky may find one which has a USB interface, but propably more expensive.
 
Maybe I should have asked the op - Is this for external voltage that you are tring to monitor, OR are you just tring to monitor/record the voltages from your PSU.

If External voltages, then follow my advise.

If Internal PSU voltages are what you are tring to Monitor, Follow saint19's advise. I normally use CPUID's HWMonitor. Note: HWMonitor does not report the +%, or +12 V correctly on my Gigabyte P55-UM4P (otheres have also reported incorrect readings)