Lindsay, expert researchers tell us amateurs that the Nat'l Archives WWII enlistment database contains considerable errors. Consequently, take this info with a grain of salt.
Of the two possible numbers you listed, neither is shown in the database as assigned to a James M. Garner. Of the 13 James M. Garner's listed in the enlistment database, only one has Ft. Oglethorpe catalogued as his place of enlistment. His serial number is listed there as 34367389.
If this is, indeed, the correct serial number for the individual about whom you are seeking info, you may be able to get his personnel record through the NPRC in St. Louis. (They had a disastrous fire in 1973 which destroyed many records, but it is worth a try.) Info on that resource can be found at this web page: http://www.archives.gov/st-louis/military-personnel/index.htmlhttp://www.archives.gov/st-louis/military-personnel/index.html
If, as alluded to in another post, he was in the 21st Infantry, 24th Infantry Division, you can get a pretty good look at division history at this web address: http://home.att.net/~victory24/Enter.htmhttp://home.att.net/~victory24/Enter.htm
Good luck and I reitierate: I am not an expert in this field, so confirm all info suggested here with independent sources.