Well, I dl'd WSU from MS and I've installed it on my XP box. After a reboot we'll see what happens but reading some other posts on the board hear it looks quite painful to setup.
Using the info at http://www.troubleshooters.com/linux/nfs.htm
was pretty easy to setup NFS on my Linux box and was then able to mount that share on the Roku.
I did a quick initial test using an 860MB mpg2 Program Stream HD demo file. Using the time command and copying from the same file from the NFS share and SMB share to /dev/null, Linux network monitor reported the transfer averaged 2.8MB/s from the SMB share, 7.8MB/s from the NFS share. The time was 1m53s via NFS, 5m10s via SMB. That's quite an improvement in raw throughput.
ProjectX says the source file is 17.5Mbps average bitrate. Over SMB, the file was unwatchable, over NFS it's still not watchable with either MPlay or the built-in player.
Trying to watch the same clip on my WinXP machine, WMP6.4 stuttered and skipped. VLC 0.8.1 appeared to play through flawlessly. My Windows net monitor reported the filestreaming from my Linux server at an average of ~20Mb/sec.
So...I've got some 30+ Mb/sec .ts files somewhere, I'll see if the results are better on the Roku as a .ts vs. a PS.