No sadly I didn't
Apparently the only disk defrag app that I have ever heard of that got writtern for NT 3.x was Diskeeper 1! (so much for that).
As for a taskmanger style program I have just about given up. Most of the utils on the otherwise brilliant
www.sysinternals.com don't work on NT 3.x (a large chunk of the pstools included). I did hear whispers of an NT 3 resource kit with something resembling a process killer contained within... but if it ever existed I can find no links. Honestly how MS could market these earlier NT OSes as serious business products and NOT include a process monitor/killer is beyond me.
On a completely different note do the Sun JRE plugins work on NT 3.51? (for the MS IE 5.01 and NS 4.75 browsers) I can get them to install but java sites don't seem to make use of them.