ok,i see what you mean.in this case, there are 2 things you must make sure.
1.that you have administrator privilages,and
2.that the whole GTA SA folder in program files is NOT read only or hidden.(as someone-whose-name-i-can't-remember- mentioned in his pretty handy modding tutorial)
if that doesnt work sorry dude,but there must be sth i dont know or/and i haven't noticed.
At least,i tried