You can access sytem commands -- such as Windows' or *ix's sort with the sytem function call. While I do work on Windows, I've MKS utilities and a commercial sort program, so I tend not to use the Windows sort command; the commercial sort my employer uses is quite fast and has a fairly low footprint.

If you've a database system, that (as suggested elsewhere) is one way; it will no doubt have a better sort for large files than will Windows or *ix. Alternatively, if you (or your employer) is willing to part with a few (well, maybe many) USD, you could buy one of the commercial sort utilities, some of which are blindingly fast — possibly faster than the sorts included with a database system.