Hope this helps....
Quoting:
"I Confirmed, this method does work.
I was able to load my same saved games after a complete PC reformat. Importantly no actual settings on my PC changed, I used the same CD and key for XP and GTA4, I used the same Rockstar Social username and password, I also used the same Microsoft Live username and password, my TCP/IP settings were even set back to their original manual values (I doubt how much that matters).
Rather than just simply copy over the "Rockstar Games" folder from my backup into the ..../Local Settings/Application Data directory like I planned I had to tweak a bit.
It seems Rockstar assigns every new connection a unique id. Underneath the ...Rockstar Games/GTA IV/savegames directory I was given a new user folder that didn't match my old one, they look something like:
user_e0000000324jk5h234kj5h.
user_e0000000ujih34nmb34nb. Just kind of a mash of letters and numbers.
All I did though was copy the contents of my old user id folder to the new one I was given post reformat. I am currently logged in to Live and Social club and loaded at the last point I saved prior to my reformat. Assumedly, this copy/paste job works because everything in my first paragraph up there was the same.
Anyways. It appears it is safe to reformat your PC and not lose your hours of progress in GTA 4, even if they have made it a bit tricky.
(All these directories are relevant for Windows XP) "