How to improve network file performance?

I have an application that uses CreateFile() to open a file and ReadFile()/WriteFile() to
access the file. I use non-buffered I/O and large memory blocks. The application
really screams on a local disk (10MB/sec sustained) but crawls when accessing a
drive across the LAN (250KB/sec). The network and both systems are idle when
running this test.

This is a 100baseT network and usually gets about 2MB/sec sustained when copying
files using the Windows explorer or the DOS copy command. Somehow, I'm getting
eight times worse performance than the Explorer.

I've tried altering the sharing flags, buffersize, and FILE_FLAG_NO_BUFFERING,
but none seem to matter. How can I make this faster?