Believe it or not, Radio Shack sells a DVM you can connect to a PC via RS232 and log readings. I think the software is no great shakes though. But they are cheap ($40 on Amazon) and the software is a free DL.
http://www.amazon.com/RadioShack-Interface-46-Range-Digital-Multimeter/dp/B005MV15HYhttp://www.radioshack.com/search/softwareResults.jsp?kw=22-812A more industrial solution is to use a USB DVM module and some real logging sw.
http://www.aktakom.com/products/index.php?SECTION_ID=164&ELEMENT_ID=457I think Fluke and some of the other DVM manufacturers sell similar except they can be used as a handheld DVM too.
Be sure whatever sw you get allows for data storage as a CSV file. Then you can import into Excel or other programs for analysis, plotting, etc.