OK, found a nice little Seagate 1Gb HDD in the spares box & stuffed it into the main machine as D
Thought I'd keep all temporary files on there to make things tidier and easier to maintain.
Explorer/Internet Options/Temporary Internet Files/Settings/Move Folder seems to have done it for IE 5.5s tempfiles. All tickety boo. Can I now delete what's left in the old C

Windows\Temporary Internet files folder????
Now for the other tempfiles. To get some temporary files to shift ya put Set TMP=D:/TEMP in autoexec.bat. So far so good. What about apps that look for the value of the TEMP pointer rather than TMP?
For some reason you're not allowed to ALSO put Set TEMP=D

TEMP in autoexec.bat - - If you do Set<enter> it shows it xxxxxed out. WHY NOT? (I also saw this mentioned on some website but they gave no reason just said it wasn't allowed)
Okay, so I tell autoexec to call win.bat, put Set TEMP=D

temp in win.bat and then got THAT to call win.com. Success. Set<enter> now shows both environmental variables point to D

TEMP
Had to tell a few apps where to park their temporary stuff, but everything (so far) seems to work OK and the machine seems perhaps fractionally faster.
Any comments? Good idea? Or have I set myself up for later trouble?
[the D: drive is on a different IDE channel from the main C: drive]