"mount /dev/sdd1 /mnt/disk" shouldn't be necessary. You can simply "mount /dev/sdd1" and it will be mounted automatically on /mnt/sdd1. This is a nice feature of TC.
Another feature is that it will search for a directory in which to load and store extensions. Create a /tce directory on the root of any partition and TC will detect and use it. Otherwise, I think the extensions are downloaded to /tmp/tce (which uses RAM and goes away when you reboot).
It sounds like you understand the tce boot parameter. On one machine I store them in a particular directory on hda6, so my boot parameter is tce=hda6/extensions/typical. On another, I store them in the root partition of the HDD, so that one is tce=sda1. It sounds like your setup should work, although most extensions install quietly without the fanfare one is used to in Windows.
As a side note, I got TC running great on a 64MB P5-166.
Daniel