I have a Windows 7 x64 Ultimate system that I use as a server.
At the moment, RDesktop and File sharing are running EXTREMELY slowly on it.
I have other, non MS services installed and they appear OK.
I just transferred 800+MB in about 15 seconds using my code source server.
A trip to Speedtest.net gets me 25Mb down/7.5Mb up.
But If I try and copy the same file using an explorer window and file sharing, it takes hours (after several minutes of discovery, I get 16KB/sec transfer).
Every other machine on my network seems OK.