What have you got for a system?
I'm running a 2.4 P4 with a gig of RAM, and with a Radeon 9700 it runs perfectly smooth at 640x480.
If you have 512 meg of ram and a card like a Geforce 4 or MX, you might be able to get good frame rates as long as you stick to the 640x480. It looks surprisingly good at that resolution though.
Still, ultra high detail makes for some extremely detailed monsters