My system started out being just a PIII 650/100 (PII 400 is actually faster in some ways) with 128 MB of RAM and a Daimond Viper II 32MB (S3 S2000 chip), back then VIA 4-in-1 drivers were not all they could be either...
The sheep were not the cause of low fps. Turning ground clutter lowered fps (along with smoke and flying around bases). Of course now the "old" ground clutter (trees and rocks) is always on and the "new" ground clutter switch toggles the low alt textures which can really kill fps.
I understand that when your average fps is 20 to 30, 5 fps is a big difference, but I still don't believe (based on my own experience with a system comparable to yours) the sheep are that big of a hit compared to several other factors.
I initially upgraded my video card because Diamond and S3 never finished making the Viper II drivers fully DX7 compliant. When it worked, it looked really good and had plenty of speed, but nearly every game (except AH

) had flaws. Ironically, I picked the Voodoo 5 based on what was being said over at the WB site and they no longer even support it.
I feel sorry for you if you can't afford to upgrade a little since my system is already reaching its limits with newer games. At some point, AH is going to have to upgrade their graphics to remain competitive. I want to see AH stay up with technology, but I dread the day when I have to leave my Voodoo behind. It looks so good, but it is too slow to handle the newest stuff.