All, 
After endless searching on remote forums, foreign websites, and other nameless sources, I have come to the conclusion that I may just have to wait until a GTA V3.00 downgrade is released. 
Is there anyone out there that is reading this that may be a little more knowledgeable on the possibility of modding a V3.00 installation? (By now I'm sure you're aware that I payed and downloaded this copy from Direct2Drive(dot)com). 
Thank you for any input you may have. 
 
There has been a lot of research on this already, and it appears that v3.0, which is what you have, is very similar to v2.0. 
Saved-Games from v2.0 should work with v3.0 and vice-versa; however, there are no downgraders that work for v3.0, only for v2.0. 
The primary reason that v3.0 can’t be downgraded is because it doesn’t have a gta_sa.exe file, which is what’s replaced on v2.0 to make it downgradable. 
I’m sorry to say that, for now, you’re stuck with an un-modable game, at least until someone can figure out how to downgrade it. 
Credit goes to P.D. Escobar and TenaciousD. for that info. 
 
 
EDIT:  Saw this in another post... Sigh 
Happy Landings, 
FlyGuy