For windows 7 or above1)Click start.
2) Choose control panel.
3) Choose System and Maintenance.
4) View Computer details.
5) Click Advanced System Settings.
6) Choose settings.
7) Select adjust for best performance option.
8) Click apply button.
Your theme will be classic.
9) Close every thing .
FOR WINDOWS XP1) Right click on my computer.
2) Choose properties.
A dialog box will appear.
3) Click on advanced tab.
4)Click properties button.
A new box will appear.
5) Choose adjust for best performance option.
6) Click apply.
After applying your windows view will be fully classic,but your speed will increase.
7) Close all programs.
AFTER DOING ONE OF THOSE ABOVE,DO THIS :
1) Open gta sanandreas [NOT SA-MP].
2) Choose options.
3) Choose display settings.
4) Choose Advanced.
Now you must configure some settings.
5) Change the Draw Distance to lowest bar.
6) Change Wide Screen setting to OFF.
7) Change Visual FX Quality to Low.
8) Change Anti-Aliasing to OFF.
9) Disable FPS Limit.
10) Change Resolution to 640+480+32.(adjust this according to your pc resolution)
11)Close Gta sa and open samp.
12)Connect to server.
And one more thing, install any fps boosting apps, here is the link of my app,
https://www.mediafire.com/?kdm0sfj84fbaz8dThanks you, Hope this can help you
Feel free to ask me any time if u have any doubt abt this.