If you just want a copy of an IOS from a PC stored on a 3750, I suppose you could use tftp/FTP/RCP via the 3750's command line and copy it from the PC to the 3750. (This presumes the PC provides such a server.)

If you want to actually load/upgrade the IOS image on a 3750, there are several methods. Most use a TAR file on the PC and use Network Assistant, 3750's on-board http device manager (if already loaded) or various command line options. The configuration guides describe the latter, e.g. http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_50_se/configuration/guide/swiosfs.html#wp1258237. (Another note on command line upgrades: http://www.cisco.com/en/US/products/hw/switches/ps5023/products_configuration_example09186a00804799d7.shtml)