Step 1. Download Cheat Engine
+ Show Spoiler +
WILL NOT WORK ON BATTLE.NET UNLESS YOUR OPPONENT USES THE SAME xSPEED AS YOU.
Step 2.start starcraft
Step 3.attach the engine to starcraft.exe
on the cheatengine, tick "Enable Speedhack" and then put in whatever speed you want and then click "Set speed" (ignore the sleeptime)
Refer to pics for more help.
I have tried this method on LAN and Battle.net, but only tested this with my brother.
We both used the method mentioned above, and both used the same speed. *Worked*